So if we make it simple, what new exchange want is revenue for them, with or without support for crypto, as long they can get paid for listed coins/tokens, they wouldn't care about how many volume in their site, well, actually they can get fee from trading activity but new coins/tokens will always come so it can be advantage for them.
If an exchange has no trading volume or it's very low, they will not be able to ask for a fee to list a token or the fee will be as low as the trading volume, both things are related.