Russia Ukraine war, page-241659

Why is the Ukrainian military using it's best tanks to invade Russia, instead of protecting and "re-liberating" their own lands?

The bargaining chip objective has failed.
The "forcing Russia to pull it's troops out and stop their advances in other directions" failed.
The PR stunt has run it's course.

Is Zelensky a Kremlin agent? That's the only explanation I can think of which would explain throwing the remains of the best parts of the Ukrainian army at something that achieves no strategic objective.