I attracted a good answer. It turns out that after Ukraine changed sides with their revolution in 2014, Russia was afraid for their control of the black sea from Sevastopol and that’s why they invaded the Crimea in 2014. That is possibly why they started the invasion, so they could gain a strip of land to sustain their activity there in Sevastopol.
Existing parts of Russia already border the Black Sea, is there a reason Sevastopol as a port is so highly valued? Like, can’t they make an artificial port or something off Sochi?
Edit: on closer inspection there is already a city in that area that already has a fairly substantial port capacity: Novorossiysk. And it’s in Russia proper, no need to get all worked up over Sevastopol.