Easy, tokens are supposed to be for perk and bonus hunters and those who trade short term
Bitcoin and Ether for those who also wish to hold long term, in the end at least with Bitcoin one can cash out in more exchanges, deposit onto most of casinos regardless of the price, that is the charm of high liquidity.
Yeah casino tokens are limited in number of ways, but Bitcoin,, on the other hand has a universal acceptance and bigger liquidity that make it burn into any transaction. 100% of casinos accept Bitcoin deposits even though they may have their own tokens, but because of the dominant feature of Bitcoin, it is always number one on the payment method of most casinos.