The other way to have increased liquidity in an exchange is attracting market makers to the exchange by giving competitive trading fees for giving liquidity to the exchange.
I agree, that's why some exchanges set maker fees lower than taker fees
(maker-taker fee structure)they do it to draw interest of traders to add more liquidity to order books
and tiered fees based on user's monthly trade volume helps to keep user loyal to an exchange
This is where the game changes yet competition on exchangers is pretty tough.So making some alterations or change on maker-taker fee would be crucial.
If they do set out lower then this would be main appealing to traders yet anyone do really able to achieve maximum profitability without being affect by these fees.