It has to be a geography thing. Of the 8 teams with fewer B2Bs than Boston, only one (Atlanta) is in the Eastern Conference. Of the 16 teams with more B2Bs than Boston, the ones from the West are the Clippers, Blazers, Rockets, Grizzlies, and Mavericks.
Your perception is screwed if you think the Celtics are playing a lot of back-to-backs, considering a tad more than half the league has more.
Last season, the Hornets had the fewest with 16, while Charlotte and Chicago had the most, at 23. Boston had 18, the Lakers had 20.