I think the unwritten rule of NBA officiating is that you can take 19 steps as long as you stay in rhythm. (That's why they didn't whistle LeBron--he stayed in rhythm.) If you make a move that looks clumsy or awkward, they will call steps every time, even if you are well within the 1.5 steps allowed.
I'm not defending it. That's the only explanation that makes any sense to me.
NBA officiating is far from perfect. However, it's far better than the college game. 40-60 fouls/college game is absurd and it's destroying the sport.