My assumption was made because I personally know five other foreigners who have faced the same issue as me, where their additional KYC requests were rejected. Interestingly, my Thai wife and her daughter have not yet been asked to provide any additional KYC information. I asked my wife to inquire among her Thai friends, and none of them have been contacted by Bitkub. Based on this, I speculated that the authorities may be making it, for whatever reason, difficult for Bitkub to serve non-Thais, similar to what happened recently with PayPal.
So nothing to do with Thais-do-not-want-us-here. Surely it is a matter of new rules and regulations imposed by financial authorities that requires Bitkub to jump through some additional hoops. Bitkub is probably not happy with that, as it will cost them customers and turnover.