There are absolutely no guarantees, this is why as much as possible, you try to avoid platforms with strict KYC. The problem is, most casinos not implementing strict KYCs are only good for a couple of months before they close, either because they are a scam site or that they are ordered to do so by the government. Mishandling of KYC documents is also a valid reason to raise, and we don't know anything whether our personal information is already being sold to a third-party or remains safe at the hands of the government. Whatever it is, KYC remains to be the necessary thing to follow, but we're too conflicted in actually doing it because of a lot of bad things that is associated with completing the said requirement on most casinos.
You are very correct, when scammers know that people are avoiding kyc, they will use it as a bait to attract people to their scam casino which doesn't last long. When they perfect their plans they will immediately exit the market and return with another domain to continue their scamming. The best practice is to be patient and find a reliable gambling site and stick with them.
Op said that gambling sites should investigate the sources of income of the gamblers. How will that even be possible? Even the kyc won't help because many people complete identity verification with fake or stolen identities.