Some crypto businesses do accept zero-confirmation transactions. But they take some precautions to make sure you won't be able to cancel the transaction and even if you do, it shouldn't cause them any financial damage. In case of casinos, for example, they will instantly credit your account only when the transaction is non-RBF.
At least one casino (Sportsbet) lets you deposit RBF zero-confirm transactions (from my experience) so I'm curious to know how many casinos actually have this risk-assessment tech deployed, and whether they make it in-house or use one from a provider (and who?).