Because its easy way for them to earn even more money. And traders like them because its a way to save on fees
That's also become the best way for the exchange site to give the reward for its community too.
The exchange sites were giving so many abilities to its token. The users are also getting more advantages by holding the tokens that are issued by the exchange site.
It's not only the exchange site care about the money but the exchange site is also care with the community that supports the team to develop a proper platform.