It was banned by the federal government

Not exactly. The law was weird, and that's why it was overturned. It didn't make sports betting illegal federally, instead it prevented states from "authorizing" it, which the petitioners argued was an unconstitutional intrusion into the lawmaking ability of states in that it prevented them from repealing laws against sports betting that they had previously passed.

The full ruling is at https://www.supremecourt.gov/opinions/17pdf/16-476_dbfi.pdf, and the last paragraph sums it up: "Congress can regulate sports gambling directly, but if it elects not to do so, each State is free to act on its own".

The SCOTUS ruling didn't legalize sports betting; states chose to do that themselves once they were no longer prevented from doing so. Congress could ban it nationwide today, and probably they should.