Because they're not UBI, they're featherbedded kleptocracies. Everything keeps running provided they have the income to maintain the corruption and trickle down at every level to the officials who expect a varying scale of bribes and kickbacks.
The system though ultimately is designed to ensure wealth flows upwards to the top, not to actually build a capitalist economy with a guaranteed minimum living standard.
But the effect is same. At the end of the day citizens survive on state welfare. Nobody said UBI is contingent on a corruption-free, western democracy.
But do you expect any different from real UBI without any empirical evidence? It is easy to speculate that citizens would achieve some magical enlightened higher state of being where they would dedicate themselves in pursuit of the arts and entrepreneurship. The reality may be that most would just spend the day gaming and smoking marijuana. By discounting the Arabic states, it is doing social science and economics a disservice just because they do not fit the expectations of advocacy and academia. I don't think endemic corruption means that the Arabic model have absolutely zero value, they are hardly the only wealthy country with pervasive grift. Letting political views and biases leak into social science and economics is not helpful at all.
The system though ultimately is designed to ensure wealth flows upwards to the top, not to actually build a capitalist economy with a guaranteed minimum living standard.