From a team's perspective, losing somebody permanently - like Collins for the Packers - messes things up because it is can't really be planned for like age and contract expiration.

From a player's perspective (and I expect what I say to generate a bunch of hate, but I'll say it anyway), they are paid absolutely huge amounts, even lesser players, to go out there and play a game that many of us would love to play for nothing or a tiny fraction as much. Injuries, even career ending, even injuries that mess up their future lives, are the risk they take. They know that risk going in, and if they don't want the risk, they can just quit and get a real job for a tiny tiny fraction of what they make in the NFL.