I don't think pension factor comes into the equation, at all. Teams aren't cutting guys because they are close to getting their pension years in. Guys get cut because they aren't good enough to be impact players and they don't have the upside left to be better lottery tickets than the younger players with less baggage. Plus, the NFL now allows for veteran salary cap hit benefit once a player has 4+ years of experience, so they only count as a 2nd year player. That is what really matters for NFL teams. That changed a few years back, so before that, sure, that was an issue, but it isn't now under this new CBA.
Also, the money is what makes it worth it and why most of these guys do it. What are the other options for most of these players, if they weren't football players? Let's even consider their options as a college grad and just disregard the fact 50% (probably much higher) wouldn't have degrees at all and 90% wouldn't have degrees from equivalent level Universities, if it wasn't for football. Just that alone is probably worth it for most of them.
What do you think they make with, mostly, trash degrees and low GPAs? Maybe average career earnings of around the median income? So an average of like $55k a year for 40 years? So $2.2M? They can make that chasing the minimums in the NFL for 3+ years and they still have 35 years of a regular job. For most people, that alone would be worth it. However, there is also the upside you can make enough money in 5 years that you and your family never have to work again.
If you are the #32 pick you get $8.5M over 5 years, guaranteed. That isn't the ceiling, but even that, for 5 years of work is astronomical. That is the kind of money where you can easily live the rest of your life without having to work at all AND leave wealth to your family.
What careers are "worth it" if football doesn't qualify as one? Are they only steady, secure jobs where you have almost no chance at life changing money, but also have very little downside?