Stablecoins changed one small part of crypto casino play: the session amount became easier to read. With Bitcoin or Ethereum, the coin can change value before a player even starts choosing games. With USDT or USDC, the payment side feels closer to a dollar reference. The game can still vary from spin to spin, but the coin is no longer adding its own price movement to the session.
Stablecoins moved from exchange accounts into everyday crypto payments because that reference point is easier to hold in mind.