Governments do run experiments sometimes, quite a lot of experiments on UBI have been run for example and we have good knowledge on whether its introduction would improve society. But I don't feel like leadership particularly cares about evidence and the right thing, they are far more idealogical than that and tend to gravitate towards policy based evidence from thinktanks and other powerful sources that produce bad science but the results they want to see.

The populace doesn't have much in the way of alternative choices for politicians that would follow the results of actual experiments nor fund them, its not really an option being offered, I think partly because its a tough sell compared to "we will do X". "We will test a variety of options and then do the best" requires more trust and its a low trust environment.

I think the UBI experiments were one-sided. They may have proven that the receivers have profited. But did they show that the givers profited as well, or at least did not suffer enough to significantly reduce their economic output and therefore risk the financing of UBI?

You'd need to check something like take a group of high-earners, increase their tax rate by say 100%, increase their cost of living, and validate that they neither leave the experiment nor work significantly less.

Honestly this is because an enormous segment of the population has offloaded their critical thinking skills and moral evaluation to large media conglomerates, who mostly serve the interests of those at the top who would not benefit from these things.

If a politician does want to shape policy based on research evidence for what would improve society, this captured segment of the electorate is weaponized against them.