Effectively, they are at 20 (with today's knowledge) given 15 years at the top of the most popular American sport. They make hundreds of millions in the process (possibly).
By the time they are 40 or 50 they might be a vegetable or have committed suicide, but honestly how is that different than any other job? It's a decision they make for celebrity and money and competition - how many CEOs have killed themselves via overwork?
On the other hand when Tony Dorsett says "I didn't expect the end to be like this", it does shock you to the core. And it's a sport that kids should not be playing.
Football is a violent sport but that's what makes it magical....you can't have men that are 6 foot 6 and can run a 4.3 without it happening. But you can't get something that completely tactical and brutal without those dynamics. I'd hate for football to die.
There's also genuinely good owners in the league; hate someone like Jerry Jones all you want but he has taken care of all of his former players and is one of the most giving people in the league. There's also some really brilliant and good front offices (New England or even Dallas with Will McClay).
....also regarding Kerr, he's had an amazing career.
Bulls in the 90s, Spurs in the 00s (killed the Mavs in 03 WCF), then goes to Phoenix and helps build the Seven Seconds or Less Suns, now GS. And he was a pretty good analyst! Talk about a winner.