Much of the support for UBI comes from a segment of the libertarian right which sees it as a way to eliminate welfare bureaucracy and regulation (not just regulation in the public benefit space, but also minimum wages and some others.)

It's not really a “hard left” policy, it's more a policy of pragmatic libertarians on both left and right, opposed by both dogmatic libertarians (because it remains a public intervention, if lighter-touch than the status quo policies it would displace immediately or over time) and those on the left and right with a stronger preference for government control and direction.