Why can't the war be won? The Defending military does not need to take back all captured land, just outlive the inevitable collapse of invading milita

Why can't the war be won?

The Defending military does not need to take back all captured land, just outlive the inevitable collapse of invading military or nation if the advance halts.

Many militaries have survived seiges. https://x.com/mattwridley/status/1896189511886877029