1. To blame Manning for injuries to his WRs is a stretch. Thompkins got hurt catching a ball from Brady. Might I mention Gronk. Yeah, I know, we're talking about concussions. You don't have to be catching a ball to get a concussion. Welker, Stokley, Collie...they're all small guys getting beat by guys that have 60lbs and 5inches over them. So their heads are at a "convenient" location.
ps. I hope Amendola and Edelman be extra careful.
2. It's not easy to "just retire". For a lot of these guys, it's their whole life and when you've worked your whole life to get to this point, sometimes nothing else matters. Some get lucky and some never recover from a failed career. It's the same with boxers. All they know is how to fight. And when that is taken away from you, you feel like a worthless human being. I'm not saying that is right but that's what a lot of guys think.
Disclaimer: I'm not an athlete but i'm a musician and I have many many friends who work super low wage jobs they hate just so they can get by and continue to "stay in the music business". To give up a dream is worse than not trying to hang on to it, sometimes at great cost.