buffer zone, natural resources, water supply for warm water port, delusional bragging rights, access to do more of the same to moldova and surrounding states.
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.