Traditionally Japanese pitchers threw a lot more than American ones, even if they only went once a week in games. Their side sessions were long and frequent. The idea is that you train to pitch by constantly throwing, just like a jogger becomes a marathoner. I don't know if that's still the case.
Right, so it's probably more about constant ultra-max-effort over thousands of reps than it is about the number of reps. Distance runners (who DO get cyclic ligament fatigue injuries anyway) don't compete to pound their feet into the ground as hard as they can on every step.
I know this has been referenced a bunch before, but it just feels like where this is going is that pitching is becoming a fungible commodity that doesn't get paid well anymore. Velocity can be taught and it pays, but it also kills, so you burn out before you escape arb years and actually get paid. Teams can get similar results by continually throwing max-effort elbows into the grinder for minimum money, and the youth baseball system now is built to help them do this. This means that other parts of pitching craft (like adding a strong 3rd or 4th pitch, or learning elite command) don't get as developed, and there's a sameness to every inning and game.
From a fan perspective, it feels less than ideal, because there's less continuity and story to it. 10 indistinguishable relievers that throw upper nineties and will likely get hurt and be replaced by 10 different guys in 1-2 seasons anyway is hard to get hooked on. This is economically optimized, but I think it's rare that optimal economic outcomes are fun things you seek out in your spare recreational time.