not all people feel comfortable handing documents to strangers on the internet, did you know that they can take your documents and commit crimes and you are guilty of crimes you didn't commit and it's all because of someone from the anonymous site where you did KYC and Did he sell your documents to a criminal?
Yes, they can do that and there is also the risk of their database getting hacked and your personal information/documents getting leaked all over the Internet. But why would you send your documents to an anonymous company in first place! You should pass kyc only on trusted casinos with good security measures. You are going to send your money after all, so à minimum of trust is needed.
Sometimes we have to review every terms and conditions because they have been changed/added without our knowledge, for example previously no casino asked for KYC verification before the casino complied with regulatory authorities, but after the new rules were implemented there was no announcement to the community before gamblers knew about it during withdrawal.
Any reputable casino, or business in general, will notify its customers about any change in their ToS before those changes take effect (usually no less than a week).