> SatoshiDice is a dapp that was built using bitcoin.

But SatoshiDice was not trustless; it was only provably-fair. By sending your dice bet to satoshidice, you were trusting them to actually pay you if you won instead of just keeping your money (though you didn't have to trust that they were using a fair die).

An on-chain dice contract is completely different, because there's no central operator that you have to trust to pay out the winnings.