I haven't broken a string in over 20 years (and I still always carry a spare set every time I leave the house

).
Seriously, I wonder if it's a youth/experience issue because I'd still say I hit the strings pretty hard from time to time. I even still own one of the basses I owned back then (not that I play it much) - but I haven't broken a sting on it since the mid '80s.
Maybe we eventually learn to play with the energy focused differently (efficiently) over time.