Alot of them do die young, or develop seriuos life threatening problems that causes them to go to the hospital for one problem that leads to another, and another. It doesn't happen to everybody but it does happen alot more to the big huge slobs who don't lift. Having a disproportionately large belly has been proven time and time agian to lead to health issues.
They do die also. It seems at least one basketball player a year dies on the ncaa court from a heart issue, that would not have happened if they didn't play ball. I know if I played college basketball and some doctor told me my heart couldn't handle it I still would, and push it to the limit.
Athletes die in other sports also.
Researchers need to look for direct correlations, however normal people need to stop. The reasons for dying are as complex as the body itself. Many of the powerlifters that you think are healthy didn't start off that way. For the longest time the motto was eat everything you possibly can and lift heavy. If you did this in your teen years and decided to become healthy last year, your body still may have not adjusted. Steriods in my opinion does have an effect on something, if at one time in your life you overdoesed on that theres no telling what that could effect.
Lets not forget the binge drinking on weekends and cheat meal days of 2 pizza pies. One day of clogged arteries just might effect your heart when your doing 20 rep squat with twice your bodyweight for 5 sets. Eat fish year round who knows your genetics might be extra sensative to mercury. Maybe your middle school was the first to experiment with lead/abspetos(I have no clue how to spell it) paint. It can be something as little as lungs can't handle training in denver, taking a flight out and competing in Jamaica. Theres millions of reasons.