"but Ukraine has sent their best to protect this location" They haven't, in fact, their best brigades are currently in Kursk, why there? Well, there are 2 reasons - one, at the negotiating table, Ukrainians could use occupied Kursk territories as a way to trade it off back for occupied Ukrainian territories. The second reason is to cut off gas supply to Europe and also to capture the Kursk nuclear powerplant and Kursk city- both which are highly unlikely.