In this scenario, by assuring the coup plotters that the U.S. will keep funding the war as long as they keep fighting it, as opposed to cutting bait with the coup as an excuse. The coup plotters would then accuse the deposed government of treasonously planning a surrender (a mischaracterization, but that's par for the course) and portray themselves as acting in the national interest. They then keep the status quo of the war, with just a change in management. This would all fit neatly with the anti-Russia/pro-U.S. propaganda Ukraine has been subjected to. Any Russian objection would be written off as lies.

If Russia tried to support a coup government, that government would be branded as treasonous even if they sought to act in the best interest of the Ukrainian people. The U.S. would immediately seek to discredit and destabilize the coup government, and a lot of Ukrainians would listen as they're fighting a war with Russia.