Why not? All the research I've seen indicates that a 5-man rotation offers no health benefits over a 4-man rotation. The Dodgers began the 5-man rotation because they had five good starters, not because they wanted to prevent injuries. No-can-do 4 man rotations any more. Ever since the Pitcher's Mound was raised, pitchers have had to throw more breaking stuff and fewer fastballs. The breaking stuff is harder on the arm, so you can't do the 40+ starts like they did before the mound was raised. Studies have shown that the higher mounds of today lead to more injuries among pitchers (http://www.eyedoctornewsletter.com/pitchersmound). After the 1968 season, the mound was lowered from 15 inches to 10 inches. And MLB began to check mound heights, which often varied widely from 15 inches. Dodger Stadium in the 1960s was probably closer to 20 than 15 inches.