Stable coins also have a stable transaction fee, especially if under erc20 tokens.. I guess altcoins with cheap fees are still favorable, especially for gamblers with small bankrolls in gambling.
Stablecoins especially those that use ERC20 platforms will really need very high fees for transferring. At least, we need more than $10 commonly when transferring stable coins from an exchange to others or to the gambling sites.
So far, if there are more altcoins that have lower fees, gamblers will prefer using it.
Some that are probably favorable are likely XRP, XLM, and also LTC
If it's coming from an exchange, then it depends on a certain exchange too. But the cheapest according to my experience is XRP, you don't need to pay a whole 1 XRP to get your transaction to confirm fast, even 10% of 1 xrp, it will confirm your transaction automatically. In addition, it's liquid, so any exchanges you like to trade it, you can do it without a problem.