I think this is related to Sportsfreak's earlier point about less contact. There is less contact because players are trying to hit home runs. Fans love home runs, so the game has evolved to increase the numbers. As you said, the mound is lower, ballparks are getting smaller and I believe balls are juiced. Players are now hitting more home runs because it's easier to get enough of them to make the sacrifice of less contact worthwhile.
In response, in order to avoid home runs, pitchers are throwing max velocity, increasing spin rate and throwing more types of pitches than they did in the 60s. This reduces contact so as to make the home runs less damaging with fewer base runners. It also makes it more difficult to string hits together which further motivates players to swing for the fences. The trade off is that pitchers are not able to pitch as many innings and are getting injured at perhaps greater rates despite more advanced training and health care.