It is a great position to hold and fight in, because the area is pretty empty of civilians. And russia must avoid ukranian (russian in their eyes) civilian casualties, to not loose the little popular support they have for this war.
And neither side will be so stupid to directly bomb the remains of the reactor, but I think it would need a serious direct bombing, for radiation to leak out. I don't think there can be still a major uncontrolled chain reaction. The worst that can happen under normal circumstances, is radiation leaking out.
(but all this is from the back of my head knowledge, about documentaries about chernobyl, I might be wrong)
It's just that somebody has to be in control of it, and the Russians can't or don't want to depend on Ukrainian forces to do that right now.
Then he would just shell and flatten all the ukrainian cities. Russia has air superiority as far as I know.