I mean isn't it so small that a single artillery barrage or tochka-U would hit everything on it?
Ukraine lost a shit ton of ppl trying to launch attacks to take it back. Presumably, Russia realized that its easier to just defend it from air/sea and not put soldiers on the little rock.
About why they retreated from Kiev direction, as much as some ppl say its because they were overwhelmed, I don't really trust that. Russia barely lost any troops in the North, nearly all losses were in the south (Mauripol) and Donbass.
Conventional wisdom says you need a larger force when invading with the intent of total annexation. Look at the Iraq war for example, US surrounded and had about 1.1 as many troops even with Iraq's deficient command and non existent air force.
Russia had 150 000 to Kiev's 400 000. It is just stupid to push under such conditions, unless the goal of the Kiev push was to force all the elite Ukraine battalions to abandon the south and Donbass, giving the LDPR time to mobilize their soldiers.