"without ever telling us why" indicates that they do not know.
Sometimes one may be able to take a good guess at where one did not comply with the letter or the spirit of a certain rule, but still not be told which specific violation was detected and triggered a ban. Both are useful information and the question could have referred to either.
We do not know. I am sure the banning email must have mentioned something but it was far too vague and non-actionable for us.