[Rdd]

Not sure of the full reasons (and why they are not even later to allow for a game fully in prime time) but as you alude to there are only two Sunday game windows in the divisional (QF) and conference championships (SF) rounds, so they are not trying to squeeze three consecutive games in. Also, because they are knockout fixtures, the games must be won on the night, so they do allow a bit more time between for the possibility of overtime.