Or the flip side. Russia is trying to take control of land, but what's the point if you level everything and make it uninhabitable.
Also, Russia has actually gained a huge border directly with NATO as a direct result of this war. It's really backfired in that regard. Finland wouldn't have joined NATO if Russia hadn't shown how dangerous they can be. They were perfectly happy with the status quo until this.
Launching a genocidal war for such goal is as laughable as all the other reasons that get stated.