Juxtaposing two threads.....tackling is not what it used to be.
When you look at many of the Butkus' tackles, today they would be called spearing or targeting. That is simply how tackling used to be taught. It is not longer taught that way for a couple of reasons:
- Leading with your head, especially if the tackler dips his head leads to increased concussions and neck and spine injuries.
- If you teach the 'old' ways of tackling, and you are a coach, you will get sued, lose your job, etc..
Further, most of the concussion studies of late would seem to indicate that the number of hits is equally important in leading to CTE as the big hits. As a consequence, coaches are discouraged from tackling drills in practice.
When teaching tackling techniques, this video
https://www.seahawks.com/video/2016-seahawks-tackling used to be prevalent. I would have to check with my son to see if it still is, but I would imagine it still is...or something close.
In regard to the passivity of CB tackling, I think it boils down to physics. Unless they commit to having a reasonably high rate of speed/acceleration in the attack, they are going to get run over. You are either the windshield or the bug and most CBs would rather try to punch the ball out, push someone out of bounds, or otherwise avoid a head-on (shoulder on) hit.
Butkus, Nitschke, and most other of the players from the glory days would be kicked out of the game and penalized if they used the old methods of tackling.