There were talks about a Zapo offensive meant to cut the land bridge to Crimea. If that happens, the Russians will have to pull back to Crimea.
Since the Russians are highly mobile, they don't need to defend every single nook and cranny in the region like the Ukrainians are doing. The cost of that is more dead soldiers, which is why the casualty ratio is so lopsided in favour of Russia.
Pulling back also forces the defenders out from their hiding spaces and out into the open, where they can be killed easily. At the same time, the Ukrainians will have to throw more bodies at well-prepared Russian defences while waiting for the Russians to renew their offensive.