Maybe they've got the plan of creating their own coin. Possible as a beginning of such a plan they might be adding more new coins. Some coins don't even get listed on the exchanges, people holding such coins might get benefitted if it gets added here.
Adding their own token doesn't really attract player. I mean that token is created only for purpose like free faucet when they want to test the site. (PLAY on cryptogames, WIN on windice as example.)
AFAIK, No gambling site ever have listed such token/coin which didn't listed on exchange except their own token.
It depends on the feature of the token obviously.
If it just a playmoney to play the game without any other features then for sure it wont attract players.
But if the token is something that has some attractive features or function such as:
- The one on Bitsler, where players can use it to participate on contest to win real money.
- The one on Chips and some other sites, where player get the token by wagering then player can stake it on the vault to get some earning.
- Exchangeable token where players are able to convert it into real money.
Those features will attract players as players has the chance to earn or win something from the token.