UBI has to be funded by taxation on the rich. If you give Mick 2k/mo but tax him 5M/mo i think you're coming out ahead, and you're avoiding all the bureaucracy of deciding who does and doesn't get the 2k... Which would be large, complex and prohibitive.
I'd rather not set a precedent for it being means-gated. Some people who don't need it getting free money is an acceptable tradeoff to ensure that everyone who needs it does get it.