Having a 33% chance at having a pro bowl safety for 14+ games is far superior than keeping a roster spot for the Roberto Wallaces and Marlon Moores of the world. Call me crazy
And it's not like injuries are some sort of exact science in the NFL. Many players get hurt for a few years in a row and then are fine the rest of their career.
This is a pro bowler in the middle of his career that doesn't even cost a draft pick. You take the chance. Nobody is saying there isn't a risk, I'm just saying the risk is worth the possible reward.
This is what many NFL employees and you seemingly don't understand. Life is on the wire, you need to constantly take chances to get a championship team. What's the worst that happens? He gets hurt again and we cut him the next offseason. What's the best that can happen? We get a pro bowl player for free.
YOU TAKE THE CHANCE.