Few basketball games are blowouts. The logic of sitting your best player(s) in foul trouble is to hope that your bench can keep the game close so that your best player can win the game in the end.
I think the idea is that having a lead early versus late gives the opposition a more clear goal with the time to come back.
Basketball games and seasons are very long. Players won't be focused in the entire season or for entire games. Having a deficit to come back from, with the time to do it, gives them a clear objective to focus in on.