It's not really that odd, actually. The schedules are structured differently. In the regular season, tomorrow is guaranteed for the vast majority of the season. In the playoffs, it's not. And in the playoffs, you don't need to save your workhorses for the long haul of the regular season and then also, hopefully, the playoffs. That's also why you see starting pitchers working on short rest rather frequently in the playoffs but rarely see it in the regular season.
The regular season is a marathon. The playoffs are very much a sprint.