What do you mean by exchange ban them? Does the exchange site be able to detect if the Bitcoin came from mixers? I think it depends on the exchange whether they have on their terms and condition whether they ban those coins or not.
I am not from any exchanges but I think Exchanges analyze transactions. Here is an
transaction, which probably joined a coinjoin. So, explorer is analyzing the transaction and marking it as coinjoin transaction. So, it's not difficult for exchanges to identify.
So, after reading some articles, I read CZ's explanation. He said exchange doesn't freeze users fund for using coinjoin/mixer. They have to abide by the local authority. Here you can read full article and explanation from CZ.
1.
https://blocks99.com/binance-issues-coinjoin-warning/2.
https://www.binance.com/en/blog/414733786553217024/CZ-on-Regulations-Exchanges--Privacy