People that are using USDT to gamble may prefer to hold USDT instead which is not a coin of value as it is only pegged with dollar. Gamblers will most likely lose and that is not bad at all. I also noticed that I do not like to use bitcoin to gamble, I prefer to hold it instead while I use USDT to gamble.
If your main intention is just to gamble and you're using crypto as your platform, then USDT is the most practical choice, so you can focus on your strategy to win instead of stressing about price fluctuations. But USDT only came in later. Back in the day, it was mostly just popular games like dice, very common at the time, and then eventually, sports betting caught on. Bitcoin was really the main coin being used. Not sure if that’s still the case nowadays though.