I think they just lack the sophistication to do it any other way. According to their own doctrine, they should be trying to flank and encircle a city, cut off e

I think they just lack the sophistication to do it any other way. According to their own doctrine, they should be trying to flank and encircle a city, cut off enemy logistics and reinforcements, and suffocate the defenders. But in most cases they were unable to to do, so they just default to pure destruction. It's just simpler to bomb everything that could shelter Ukrainian defenders. Russian artillery and aviation is not really known for their precision. There is nothing surgical about their approach. They are just throwing tons and tons of explosives at urban centers until they are stopped or there is nothing left to bomb. I think the siege of Mariupol was the only somewhat successful Russian urban operation in this war.