I don't really understand how that is possible. If there's a casino managing the funds, no matter how reputable it is, it is still centralized.
It's possible to build some a "decentralized" casino, in the sense you're interacting with a "smart contract" instead of a centralized party directly. It's not super practical without a (centralized) entity that manages the smart-contract (and profits from it!) but they can offer some pretty cool benefits to players.
And that benefit is "trustlessness". In the sense that a normal bitcoin casino offers "provably fair" which means "it can cheat you, but you can detect if they do" while a trustless setup would mean that they can never even cheat you (if you trust the software, and there's no bugs, that is).
But "decentralized" casinos also have a huge disadvantage: They have an absolutely horrible UX, and they are typically on-chain which means slow and expensive.
So that raises the question: Can you offer trustless gambling, while not totally destroying the UX? And I think the answer to that is actually 'yes'. You can use a lightning-like system, where the balance is dependent on some auditable event that can be enforced by the blockchain. So you can keep gambling with the site (offchain!) and then only in a dispute (or when you're done) dumping the last state for the network to enforce.
The only problem I really see is that it's *insanely* complex to implement, compared to a normal casino -- and players probably don't care that much.