Crimea doesn’t bring much of advantage to any side, it sits there like a civilisational Wonder in AoE, it’s ports just increasing the logistical strenght to the fleet, but not that much.
But it’s a big and important point of Valdemars political standing, and he won’t like it to be theatened at all. As it was a big win for him in the 2014. He’d not like to lose it.
But the thing is, it’s hard to logistically support it. The landbrindge is vulnerable, so this new bridge was built, this project took years, but this semi-island is still isolated and can be cut off, so it’s harder to defend it.
I think, if Ukrainians manage to take any new land soon, it would be Crimea, for it’s easier to cut it off from all channels of supplies than those dug in lines on other fronts.