Because its easy way for them to earn even more money. And traders like them because its a way to save on fees
Basically there is no easy way to make money, because all methods obviously cost even a little, so the merchants will follow the methods they can outsmart so that the costs are always low in all respects.
unreasonable reasons, it is not because it wants to make easy money, but indeed an exchange wants to have its own coins or tokens in order to compete with other exchange projects, and of course there are many use cases in it, a good exchange launching coins would be great, because it's one of the things to gain the trust of the users, such as Binance which has BNB, Kucoin which has KCS, and Huobi which has HuobiToken.