I really don't think you miss an Achilles tear, certainly not a full tear, no matter how athletically challenged you are. I don't know what sports news was like back in the day, and it's possible that Achilles tears were not widely reported out of, say, a lack of interest from the sports press ("Why is Smith not playing?" "He had to retire, hurt his leg." "Oh, OK.") but it wasn't because unathletic dudes tore their Achilles and didn't know. Coming on 15-20 years ago my dad, an unathletic dude, tore his Achilles and knew INSTANTLY.
I would have no idea how to go about quantifying the quality of training staffs, but I have a hard time believing that they're worse now than they used to be - I think the default assumption is that they would be better. AAU could potentially contribute, perhaps kids just beating up their bodies again and again while they are growing leads to a more frail body in general. But I'd probably put the first portion of the blame on the athleticism of the game today. Players get themselves stronger than ever before, and they play harder than ever before, and I think we're seeing this catch up with us in the form of a rise in injuries.
