Are you using gambling as an example here? I don't fully understand the relation. There isn't any way to gamble Robux for more Robux on the platform, and in the cases which are arguable (such as on-platform item trading), the money must be transferred through Roblox's Developer Exchange programme, which can't be done for Robux not earned directly from experiences.

If I understand what you mean correctly, then any Robux transferred between 2 users wouldn't be able to be cashed or exchanged for fiat for the same reason as above. If they can try to fake it by selling avatar items or experience products to another user, they would immediately be hit with the usual 30% marketplace fee, then have to attempt to get through manual DevEx review with what is very obviously a suspicious set of transactions.

The reason they're not scrutinised by security and banking laws is because the Roblox platform and economic system are carefully designed so that such abuse is neither profitable nor feasible, and as such there's nothing to uncover in any potential investigation.