[throwaway234287]

> what's to stop UBI recipients from buying shares of those companies to effect the same thing?

I guess they could, but even at best that would still only slightly mitigate the effects of the increasing inequality. Since stocks are a way of making money with money [1], what you could buy with UBI (or, more realistically, the much much smaller slice that's left after living expenses [2]) is obviously much less than what someone with either more to invest or directly benefiting from the company is getting.

[1] That is, for the purposes of this argument. Sure they're also a way of funding new endeavors etc.

[2] And that slice of dispensable income is also, generally speaking, much smaller for those with low income than those with high income, both absolutely and relatively.