I dont know...Lou Gehrig, I feel, was purely coincidence.
All jokes aside, I always heard growing up playing baseball in the early-mid 1990's that no one under 18 should throw a curveball. Strictly fastball and change. If that was the old adage then, and its somehow changed with so much money at stake in the form of signing bonuses, etc. with these high school kids, I can see them using these pitches at an earlier age to get an edge in the eyes of scouts. Its kind of the same thing as steroid use. Take now, get money, deal with consequences later, sorta thing.
Another theory I've heard, but no real way to substantiate it, is that pitchers pre-90's and 00's, would just "burn out" or have "dead arm" and retire at earlier ages because TJ surgery was not an option. Sports medicine is clearly not a forte of mine, but from what I've heard, there was no way to differentiate a UCL tear from a generic "arm injury" and even if there was, there was no way to fix it, so players simply retired. So really, there is no spike in arm injuries...its always been the same, but now there is just better diagnosis and better surgical techniques which players opt for, whereas before they'd just retire.