I actually don't think they've abandoned Kharkiv, and I don't think Kyiv ever really was an objective. Kharkiv makes sense for several reasons (sizable Russian population, proximity to border and located near vast amounts of natural resources) while Kyiv is nothing but problems with no return.

Ukraine being able to (at least temporarily) push the Russians from Kharkiv was huge for them, while the attack on Kyiv always seemed like just a list of targets that Russia just wanted to take out early on. Of course, I have no idea what is going on behind the scenes so who really knows.