I just started gambling on stake and managed to pass my kyc level 2 verification some few days back, I don't even know if I've made it to platinum one, so I honestly don't know what it takes to be a platinum 4 ranked gambler on stake, but my guess is that, it must require gambling with lots of funds to achieve such rank, and also consider the fact that there is a limit to the amount of money a person can make through trading, and providing crypto services.

So depending on the amount of money involved, it can be understandable why they are not accepting trading, provision of crypto services as a genuine prove of funds.