?
Russia’s hydrocarbon exports generate a substantial amount of revenue for the state, accounting for more than 50% of the consolidated government budget, clearly to Putin this is more valuable and of a greater degree of importance to him. It's over $50 billion dollars a year. The losses so far aren't comparable to this. Taking Ukrainian gas fields secures this, means Ukraine will never be energy independent.
Ukraine exporting gas would have cut into that budget btw, they had a lot of gas.
Without western tanks, aircraft and AA Ukraine doesn't have much of chance of reclaiming it imo.
Also worth consideration: