I don't know, you should probably ask Putin that. He has spent hundreds of billions of rubles taking land he doesn't need.
Now, if they sent the issue to me for arbitration, I would agree that the Donbass and Crimea should go to Russia and Ukraine should be allowed to join the EU and NATO. But those conditions are unacceptable to Zelensky and Putin, especially after all this blood has been spilled.
MAYBE after it grinds down to a stalemate, both sides will be more willing to come to an agreement, but not now.