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. Well, we just have to analyze in what way we can save money, otherwise, we will already lose money the moment we make a deposit due to high fees.
Stable coins that run above the ethereum network have to pay a fee like any other coin and that fee is variable as it needs to be paid in ethereum, I do not know if this is the case for the stable coins that are running on their own blockchain but at least when it come to the stable coins running on ethereum I am pretty sure this is the case because I have used some of them some time ago, but when it comes to gambling there is no doubt that coins that can deliver fast and cheap transactions are preferred and this is why doge is a very popular coin to gamble.