Again, I 100% don't trust Sapp as a reporter...
Also to hit this from another angle, the Raiders already got David Carr as starter, and traded for the head coaches long term project QB in Jarrett Stidham, and signed Nick Mullens, whom arguably has been the best #3 QB in the NFL and started for the Browns almost beating the Raiders last year.
The Raiders don't exactly need another QB, unless they're sure that QB can beat out the head coaches long term pet project Jarrett Stidham for #2 QB.
So was giving Kap a tryout, simply a PR stunt post Gruden comments and maybe NFL stunt, where Goodell has been known to pressure teams for PR favors.
And yes I stand by my comments that Kap was blackballed, the comparison to DeShaun Watson is non-existent, as Watson is (or was when he lasted played), a truely elite QB. Kaepernick was a system QB and the system he would for best in, was out of fad when he became a FA, and has mostly stayed out of fad.
You can't argue that there are 15 QBs better then Watson when he lasted played. You could argue there were 25 QB better than Kap when he lasted played. They're not in the same ball park of talent.
That being said, there clearly were not 64 QBs better than Kap, just no owner wanted that drama for a guy that's clearly not a QB1. Also again, the system he would fit bet with was out of the NFL, except the Ravens, whom reportedly we're going to sign him, with Ray Lewis pushing for it, until Kap's GF or Wife, for whatever stupid read went to social media and started attacking the Ravens owner...
So yes Kap was blackballed, but I think it's fair to say, his GF/wife also caused some of that... the system he beat fit going out of fad caused some of that, and maybe most importantly, the media focusing so much on QBs and Kap's unclear QB1 status caused a hell lot of that, as teams don't want drama for a backup role, as we have also seen with Tim Tebow. Nor a starting role player like Punter Marquette King.
So it's the norm for teams to reject players whom create extra media noise that could be seen as distracting when the players isn't a clear star.