I think a not insignificant part of it is they repair stuff surgically now that they couldn't possibly then. 20 years ago I'd be out of the sport instead of racing and and saying that some genius surgeon saved my elbow that was in 9 pieces.
Plus if you read the stories of guys dying on the velodrome the idea that there's a quantum difference in the dangers is simply silly. Yeah, riding on the roads is more dangerous due to phones anger and bigger cars, but that's different song and dance.