You mean like the one across Iran running from 2011? Yeah, I agree at this point we should just run it globally for over a decade to see if the result is in any way different than almost every single test done so far.

Not only that, but behaviour change depends on whether you expect the thing to last forever.

"This paper has two purposes. First, it documents the historical context of MINCOME, a Canadian guaranteed annual income field experiment (1974 to 1979). Second, it uses routinely collected health administration data and a quasi experimental design to document an 8.5 percent reduction in the hospitalization rate for participants relative to controls, particularly for accidents and injuries and mental health. We also found that participant contacts with physicians declined, especially for mental health, and that more adolescents continued into grade 12. We found no increase in fertility, family dissolution rates, or improved birth out comes. We conclude that a relatively modest GAI can improve population health, suggesting significant health system savings"

https://www.utpjournals.press/doi/pdf/10.3138/cpp.37.3.283

All in about 4 years.