If BI can't prove itself out in a smaller environment, we on no account can afford to risk our entire economy on it.
That said, I'm not saying this was necessarily a viable test of the idea. On the other hand, if it really is a great idea that is going to save civilization, it really ought to have the characteristic that it is still a good idea that is an improvement on the status quo even when applied in the small, such that everybody wants to continue the experiment and expand it, not shut it down. The slow drip of failed BI experiments, even if they didn't "really test BI", is becoming non-trivial evidence against the idea. An idea that only works if we wake up one day and transition the entire national economy at once, or worse, even the entire global economy (which the combination of "open borders" and BI could require, if "open borders" includes handing out BI to everyone who crosses the border), is a non-starter. Even if in some abstract sense it would work, we can't ever attain enough confidence in the plan to make it a rational choice.
There are certainly things that have the curve that if done a bit make things worse, but make things better if done wholeheartedly. However, there's a lot more things that people think have that curve but actually make things worse the more they are done. It is impossible to tell the two apart from here, and the abundance of bad ideas should give one pause before making a huge commitment. The twentieth century is strewn with the wreckage of economies that made that mistake, and the twenty-first century hasn't stopped, either. We can really only consider interventions that work in the small for our changes in the large. (And always keeping an eye out for the interventions that worked in the small but failed in the large!)