Why should an exchange reject a coin or frustrate it's flow knowing so well they will make money from the movement or trading of the coin?
To stay in the good books of the government of the jurisdiction they are operating in. They might lose profit from that user (unless of course they just seize the coins and keep them for themselves), but that's preferable to being sanctioned or shutdown.
To stay in the good books of the government is the best answer, and thanks for this and as you stated above, if the exchanges are I'm the side of the government, freezing a user's coins out of millions will in either way be a win situation for the exchange.