You can't host the United Nations while refusing visas to heads of government/state and other relevant people. (google translate):
Colombian President Gustavo Petro responded to the United States on Saturday by saying that the revocation of his visa, announced Friday by the State Department , violates international law and diplomatic immunity, and therefore he believes the UN headquarters cannot remain in New York.
"What the US government is doing to me breaks all the immunity rules on which the United Nations and its General Assembly are based. There is total immunity for presidents who attend the Assembly and the US government cannot influence the opinion of the US," Petro wrote on his X account.