because every system in the casino is made by humans, there is no such thing as perfect, so gambling sites often have difficulty detecting whether those playing on their sites are adults or children, even though the gambling sites already require KYC because now there are many ways to manipulate KYC.
Implementing kyc can’t stop minors from gambling, the only thing I know is that it can reduce it, their I no way gambling sites can completely fish out under age gamblers using their website, their are lots of way which kyc can be manipulated, and their are still lots of casino sites that those not require kyc before using them, underage gamblers are given free opportunity to gamble because I don’t know any way which minor gamblers will be fished out, so am sure underage gamblers will rather prefer to go for gambling site’s without kyc.
based on what I know, even in countries where gambling is legal, when casinos get a license they must obey the rules set and allowing minors to gamble is a serious violation so you must report to the authorities if you find minors gambling.
I don’t know if their will be any gambling site that will intentionally allow minors to gamble, because they know it might end up causing problem for them, so they are also trying to fish out the under age gamblers which they noticed, but we all know it’s not possible for all to be discovered, their are still some that will really be smart that gambling sites won’t be able to discover that they are underage gambler.