From HuffPost:

It is not as though they do not have the power to do so. Senate rules are not enshrined in the Constitution. Changing them requires a simple majority vote. The parliamentarian, Elizabeth MacDonough, is a staffer offering an opinion on Senate rules and precedents, which sometimes do not exist. She is not issuing orders from a judicial bench, nor is she the Oracle at Delphi reading the intention of the gods. Her opinions can be overruled, again, by a simple majority vote. And Biden’s Treasury Department has the legal authority to avert the debt ceiling all through its own legal authority.