There are cases of exchanges and gaming/gambling websites which clearly stated no KYC was required in order to lure customers in but then used various clauses in their Terms and Conditions to seize funds and close accounts. Many of those had sent KYC only to be told the legitimacy of the documents could not be validated therefore the victim first lost the funds and then lost their ID too.
Sending KYC to any website is something that must be avoided in all circumstances.
After they receive the KYC does anybody think they will just file them away and forget about them? No. They will sell them on to make more money.
I don't understand why anyone would feel like providing their KYC to 1xbit where it's not even safe to invest money. Scamming money and selling KYC is basically a double blow for the victims. This is the worst case scenario basically.
It is quite common among casinos and exchanges that they do not inform users that KYC verification may be required under certain circumstances.
In the case of 1xbit, there was probably not a single situation in which the user was asked to verify documents.