Putin doesn’t have the entirety of the two provinces he’s claiming. He wants the entirety of the two provinces for a couple reasons. First it gives him a domestic win. Second it screws the Ukrainian defensive lines. Right now they are situated in a way that Russia has to fight through towns that Ukraine can fortify to make them costly. If they use the province borders, they’re relatively arbitrary and Ukraine’s line of defense has to be set up further back, where they can force Russia into towns again. This favors Russia because in a couple years when they finish rebuilding their military they can just take the next area and tell everyone they get to keep that in the next ceasefire.