The money isn't pulled out, though. It is redistributed to people, many of whom will immediately spend it, and others will invest it in various (hopefully efficient) ways.
> Why would a national government do this?
The problem of entry and exit. Say one state like Massachusetts implemented a UBI. Then we could expect many people to move to MA from surrounding states, or do whatever they can to have a legal address there. However I think there are possible solutions to this and a state-by-state implementation is actually possible. For example, Alaska has their dividend program and I think the results from that have been quite good.
> I don't think we need to be paying anyone who makes over 50k
I think I agree which is why I'm more in favor of a negative income tax or other means-tested system than true UBI. But if I were to argue in favor of an "everyone gets the same" program I'd say something like, implementation is somewhat less complicated, or it's easier to explain to the public.