In addition to the other replies I also thought that at the time it was a convenient excuse to play both sides and ban the_donald without alienating a huge part of the right wing on the site. A lot of reddit chuds don't actualy care about t_d given they all came back/remained on worldnews or the Ukraine subs.

There is a whole lore about leftist subs getting co-opted and becoming irrelevant over the years which is why they don't get banned e.g latestagecapitalism.