https://phys.org/news/2018-07-short-tumultuous-life-major-league.html

"We used pitchers in the 1980–1981 season because that gave almost everyone enough time to finish their careers," says Swanson. "But we excluded those who had interrupted careers, such as those who played for a bit but might have been sent back down to the minor leagues for more training or because of injury. We wanted to look only at uninterrupted careers in the MLB, and it turns out that, on average, they're really short."

"It may be that there's so much competition to get into the Major Leagues that we end up with a lot of injuries," says Swanson. "A lifetime of baseball has gone into getting to that point. One thing we discovered by testing our analysis of 1980–1981 with a forecast for 1982 is that there is a huge amount of turmoil in a pitcher's first year or two." We could see this because it was the transition from one or two uninterrupted years in MLB to a second year or third where the forecast was least accurate. Once a pitcher survived the first two or so years, the forecasts were quite accurate.