1) The pro-Russian government of Ukraine was ousted in 2014, and was succeeded by a pro-Western government headed by the pro-European Poroshenko. The latter lost in his re-election bid in 2019 to Zelenskyy. Im guessing Russia was quite happy to see Poroshenko ousted, and assumed the non-politician Zelenskyy would be easy to manipulate back into Russias orbit, only to find it wasnt going to be the case.
2) I think one is missing the big picture in assuming that Putins machinations with the U.K. and U.S. had much to do with Ukraine, except as an interim step. The whole point of enabling Brexit (and encouraging similar movements elsewhere in Europe) and Trump was to undermine, respectively, the European Union and NATO. Im sure he hoped that Trump would remain in office and eventually dismantle NATO; with that gone and the E.U. splintered by nationalist dissensions, he certainly would be able to easily take back Ukraine, but he would also be able to do so to the Baltic republics and the rest of the Iron Curtain countries. And maybe more. But he certainly would have broken up the notion of a united, democratic Europe, and be in a position to dictate the course of everywhere up to the Atlantic a Russian Empire greater than the Tsars had ever known.