>>509547616
At first, they thought it would be over quickly, with minimal losses.
The point was to counteract the shrinking of the Russian population by repeating the Crimea operation on a bigger scale.

Now they're doing it because of sunk cost.
Russia still has some democratic elements, a defeat would be the end of Putin.
At the same time they antagonized the West, and it's obvious whatever is left of Ukraine in the end will belong to the West. So they have an incentive to take as much of Ukraine as they can while they're still fighting Ukraine alone.