The majority of cryptocurrency exchanges’ revenues is coming from trading fees. All cryptocurrency exchanges charge customers trading fees; what varies is how much. As the traded volume is down by 80% from the all-time highs in December 2017, some exchanges are now attempting to diversify their revenue streams seeking more predictable results.
But even as traded volume falls off, exchanges fiercely compete to capture the largest market share. And for established exchanges, decreasing the trading fees is perhaps the easiest way to attract more customers. But there are, of course, other factors such as security, reliability, liquidity, brand awareness, breadth of offered coins, etc.