Could be a couple reasons for that:
1) The modern day reliever seems to have difficulty finishing an inning, sitting for 10 minutes, then going back out. I don’t get it; these guys were all starting pitchers as amateurs, but it is what it is.
2) The 3 batter minimum rule. A reliever can finish an inning and not have to face 3, but if he comes out for the start of the next inning, he has to. Righty-lefty numbers probably play a role here. I don’t like it, but it’s modern baseball theory; Cora is hardly the only manager doing it.