from where I come from, even if I won $1M from an online casino and let say i managed to withdraw and passed the KYC, the state wouldn't even be able to know that I won that much let alone tax it

So again, what was the point of me passing the KYC again? From the state's side, nothing!
From the casino's side, maybe there's a reason... multi accounting, playing from restricted jurisdictions etc.
That the KYC function is only for gambling platform internal factors and even though we have more gambling accounts on different platforms, each account is required to complete KYC verification. So the KYC function is not even related to different platforms let alone countries, if for example the platform deducts tax fees from jackpot winnings but maybe there is no tax report to that country, so they just deduct the jackpot winnings for tax reasons.
It is believed that KYC is needed in order to prevent fraud. After all, a person who has passed KYC will not cheat. On the other hand, KYC can also be fraudulent if a person wants to specifically and professionally cheat a casino or an exchange.