Because it rarely, if ever happens. Hamstring injuries are incredibly rare in cycling, because the limited range of movement doesn't stretch it in the way that running, and especially sprinting, do.
Hamstrings, yes, but there are times when I've thought, "if I cane it now my knee is going to go." Maybe pro-cyclists don't let chronic knee injuries fester without proper treatment ;)
Because it rarely, if ever happens. Hamstring injuries are incredibly rare in cycling, because the limited range of movement doesn't stretch it in the way that running, and especially sprinting, do.