They're too committed to it now to leave. The war will last for the rest of Putin's life unless a deal is made. It's not inconceivable that he lives for another 10+ years. Is Ukraine to fight for another 10 years. What if the men fighting don't want to fight anymore? Will Zelensky stay in charge another decade.It's been 3 years and they're barely off the starting line, it will take 30 years at their current rate of progress just to capture all of the territory they have annexed on paper.
They'll never get over the Dnieper.