What is the difference when you turn in your chips at the poker room in your city. They will usually ask for an ID. That is the only info needed since they know who you are, see you and have you on camera, unlike online shops.
Not really about cheating, more of because the governments are requiring it so that the casino can operate smoothly. I don't think the casinos will even care about your identity to be honest. They don't care about that, all they care is that you deposit something into their casino and play.
Usually casinos have a way to detect you are cheating or have already implemented the most secure way to operate their site. Also, since the casinos don't really put their money in their hot wallets anymore, and just keep a small portion in the hot wallet and the greater chunk in the cold wallet, anyone who wins big will require an approval. Hence, before anyone who cheated will be able to withdraw their winnings they will be reviewed and caught immediately.
It's very rare if not impossible to cheat casinos these days. Very rarely is there a bug that can get exploited.
Either way it's not the reason why they ask for your ID.
Most likely your deposit was suspicious and they ask and see if you freely provide it. If you don't provide it then it gets suspicious that the funds might of been acquired illegally.