Although most of the platforms that don't require KYC are still legit, some of them are not, because most of these centralised platforms always get an issued certificate of operation, which enables them to carry on their business successfully in a country, and before they are offered the operation permit, they have to agree to abide by the terms of the government. So, some of the non-KYC platforms might not have really registered their businesses; as such, they are operating illegally, and if one is using such a platform that is operating illegally, you still have to be afraid and conscious of your money because if the platform collapses or gets caught by the government, they could be charged and all the funds of customers will be frozen. While some platforms also have KYC, they don't just make it compulsory until they have any reason to do so; then they can free the victim's account and ask the person to pass KYC.
You’re right on your take regarding the reason behind centralized services requiring KYC. IIRC the main reason why this centralized services aims to get licensed to operate legally is because they are accepting fiat as currency to their service which makes them legally obligated to follow the government law in regards with fiat AML.
Decentralized services such as DeFi and real decentralized casino usually doesn’t need license to operate since crypto currency is not a legal tender or nor regulated on most of the currency. It can be considered as play money only unless the specific country already have a rules on cryptocurrency regulation like US and EU.