If a casino campaigns for KYC-free for their customers, then customers should also consider reading the terms and conditions thoroughly. The casino may include rules to request KYC only when there is suspicion about certain account activities. This is particularly evident when there are big wins or concerning betting, deposit, or withdrawal patterns.
Especially if the big wins are related to promotions that the casino is running. It may sound like the casino is trying to scam gamblers, but we do not know what schemes the gamblers are actually engaging in. There could be attempts to exploit bonus programs or abuse of several accounts.