I don't understand why would they want a risky exchange platform. Do those give more profits than reputable ones? I mean are there freebies whenever you make a successful trade?

It was first because of their variety of options to trade. Then, they made events for a free listing and some more.
What they did was not done in a blink or just because they have reputable people/companies backing them up. They are good at keeping their traders to stick to them and not look for others.
IMO, I always prefer 2 exchanges to use and the other one is Kucoin.