Western powers supplying Ukraine don’t really want to see Ukraine deep striking Russian territory for fear of Russia claiming the West is invading russia, so many of the aid being given to Ukraine has been shorter range equipment. Additionally, Ukraine has been very wary of pushing into Russian territory for the same reason, and therefore can’t really put pressure on Russian forces to move troops away from Ukrainian occupied territory. This leaves Ukraine with, for the most part, only the strategic ability to play pickup on what Russia has already captured, which is easier for Russia to plan for