That's a different matter, the team needs KYC documents to prove ownership of the account or return the account to the original user if the report is hacked. In the gambling platform, KYC documents must not be requested unless the new gambling platform requires KYC then that is suspicion.
There are several points where site owners ask users to verify their accounts sending KYC documents and it seems that only they are suspected of cheating. There have been many attempts by gamblers to trick the site, one of the problems is having multiple accounts on the same site. When the owner starts to get suspicious about the accounts activities, KYC is the thing that will answer their suspicions.
Many people do not like to reveal their personal data in the form of KYC on gambling sites because of privacy. So no need to force yourself to join a site that requires players to send KYC documents if we care about privacy.