Back to the OP's question.
My short answer is that it's everything. It's a lack of execution. It's a lack of ability. It's a lack of coaching. It's a lack of player acquisition. And its a failure of will. When it comes to the lines of the Packers, there's so many problems that you can throw a dart just about anywhere and hit an explanation.
I do think the biggest problem is the lack of will, but you've all heard that rant of mine before so I won't repeat it again. [Added as I completed the post -- obviously I couldnt stop myself]
Other than that, though, I don't know if you can even rank the problems. Though I'll try.
Biggest problem: Player acquisition. Speaking of the OL only, I have believed for some time now that for some reason the Packer front office/scouting/personnel department just lacks something when it comes to judging offensive line quality. We have had the same arguments about draft-and-develop, free agency, using high draft choices, potential, etc etc year after year. And apart from going out and picking up big name free agents, Ted and his people have after the first year given serious attention to the OL virtually every year. High draft picks, low draft picks, low- and medium-priced free agents. And we have what... Sitton the stud and the rest who go from ok/servicable (Lang) to "good grief". And nothing I have seen in the first and third games (I have to pass on the JEts game since I never saw any of it).
I'm starting to believe that the OL is doomed to woulda/coulda/shoulda unless and until Ted and company decide to go outside their current personnel and hire some new or established gurus of identifying college and used pro talent.
And it may be the same on the DL. But I think the core problems lie more elsewhere. Which brings up ...
Second biggest problem: Coaching and coaching philosophy/approach. To me, when a team shows a lack of sufficient will to dominate, the focus should start with the coaches. I don't know where the fire gets lit, if its by the head coach, or the coordinators, or the position coaches. But I see none of that will to dominate here. I see finesse. I see confidence in systems and players. I see paying attention to execution and pad level and foot work and all that. I see striving to win. But apart from a few players I don't see that systemic and reinforced and repeated drive to dominate (Daniels comes to mind, as does Sitton and, for me anyway, Rodgers).
Don't tell me you cant get modern teams to have that attitude. There are teams that have had it, and that have it. But the Packers are not one of them. Pittsburgh has had it for years; so did the Ravens; so did the Giants, all on defense. The Jimmy Johnson Cowboys had it and the Walsh 49ers had it and the Belichek Patriots used to have it on the offensive line.
I've said it before and I'll say it until I die -- A lot of those Packer players in the Hall of Fame aren't there because they were the most skilled or the best athletes for their position or system. They are there because they had that unshakeable will to dominate.
Starr is the obvious one, here. He was a 17th round draft choice, for crying out loud. By modern standards, he was half the athlete Rodgers is or Favre was. But he sustained that drive for his entire career. You could see it even at the end, when he hung on too long and his shoulder was toast and the body simply wouldn't work anymore. He ran out of gas, but he was always a muscle car of will.
Nitschke is another. I've been debating all my life with Bear fans as to whether Nitschke or Butkus was the better middle backer. But physically, talent-wise, it wasn't even close. Butkus had it all (including the will, by the way). The fact that Nitschke's even in the conversation is testimony to the man's will. He defined ferocity, indomitability, refusal to lose, insistence on domination on every play. Butkus had all of those things, too, of course. But this isn't just the homer in me saying this, if I were on the opposing team's OL and had to face one of the two, I'd choose to go against Butkus every time. Because while Butkus was Hall of Fame first-ballot scary, Nitschke
personifiedthe word.
Adderley was Hall-of-Fame talent, so was Gregg, so was Davis and probably Henry Jordan. Wood? Will defined the man. The recently-elected Robinson. Will.
The people not in the Hall -- the Skoronskis and the Thurstons and the Dales and the Dowlers and the Flemings and the Kramers (both of them). Will.
Jethro Pugh had more talent in his left foot than Bowman and Kramer had together. But when it came down to 17 seconds and umpteen below and a field of ice? They had the will.
So where did they get it? How did Green Bay manage to get that kind of dominant team put together? To make player after player dig deeper than they knew they could, to do more than they knew they could, consistently, again and again.
Okay, Lombardi was a once in a lifetime guy. Well, he isn't the only one who's had teams demonstrate that will since he died. Don't give me this excuse that it isn't possible.
If you convince yourself the only way is to be smarter or more finesse-ish or trickier or whatever than the other guy, well then you're well and truly fucked and destined to be nothing more than another contender .
I actually think Mike McCarthy has that will to dominate in him. But for whatever reason, he outthinks too much or trusts that will too little in his gameplanning, playcalling, practice coaching, whatever.
As for the rest of the coaching staff, I dunno know where it is anymore. Edgar Bennett probably yes. The last DC I've seen have it was Shurmur.
Third, ability and fitting your players to their strengths, not your system. This is even more clearly on coaching if you ask me. Yes, it can be laid in part at the acquisition people -- to paraphrase the only Wolf who matters, if you don't have chickens you have to make do with chicken shit. But if that's what you have, then use it where its best, as fertilizer, not as food. Take Carl Bradford for the most recent example. Everyone who said positive things about him said he was best, and probably by far, as an ILB. So what do they do with him? They use most of minicamp/training camp shoehorning him as a backup OLB? He may never amount to a real chicken; but you've just spent his first offseason in your care trying to prove you're smarter than all of those people who said he was best at another position. Whether he pans out or not, you've wasted a year.
Fourth, execution. Okay, maybe part of this is the chicken v chicken shit problem, too. But this team has had execution problems for years -- bad tackling, bad angles, bad blocking, etc. I am so tired of hearing that such-and-such player is our highest scored player, and thinking this player looks like mediocrity personified. If your backups are doing D-quality work and you're better with C-quality, your job should be no safer than theirs.
So I guess I'm back with the coaching staff and front-office yet again, after all. One year can be blamed on learning the system. Two can be blamed on player ability and execution. But if the mediocrity lasts for year after year after year with an occasional blast of amazingness (see second half of 2010), then the burden lies with coaches and it lies with the front office. If you're still trying to make chicken out of chickenshit, when what you really should be trying to get is some beef bulls with serious attitude, you're not getting the job done.
I remember when I was a kid. My uncle had this one bull he kept in a corner of his barn. Damn thing was terrifying. I didn't want to go near that stall for anything. Was the orneriest cuss of an animal I've ever seen. To this day I don't know what my uncle saw in him. And I don't know how many men it took to move him.
That's the kind of OL and DL will I want to see, though. Apart from Sitton on one side and Daniels on the other, I'm not sure where it's going to come from.
Ain't going to happen anytime soon, of course, so I'll likely keep bitching.
And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God.
Romans 12:2 (NKJV)