Since it's Crimea, maybe they haven't established a proper missile defense system there? Plus Ukrainian missiles do fly to Rostovskaya and Belgorodskaya oblast' from time to time, so it's not like Russia has something like Israel's Iron Dome that can catch 95% of the incoming missiles.Doesn't Russia have extensive missile defence systems that should stop this kind of attack happening? It seems like multiple rockets got through. If this war is seen in the wider context of Nato weaponry vs Russian defence I'd imagine there are a few worried generals in Putin's army at the moment.
I'd imagine that strategic points like Moscow/St. Petersburg etc. are better defended.