Because there are lots of "game" and "gambling" platform and no one have real massive usage with thousands of real users. They all will be falling in the long-term without partnerships with big gaming industry players or massive marketing. Maybe with BTC growth, they will bounce with the market.
I agree, but are there a lot with a working business, millions of users and millions of revenue already?
Yes, theres Opskins with their wax token but they got buttf$$$ed recently, when Valve stopped allowing trading of their items.