I believe it is in their ToS but users rarely read ToS of any platform they join and use.
I actually scan/read their terms after reading my replied post before replying, then scanned their ToS again and found this..
We reserve the right to verify your identity upon your gambling reaching a certain threshold, but we maintain discretion to verify your identity at any time.
So yeah, it's clear now. But just like other says it's the marketing policy issue ehich