Intentionally targeting civilians isn't war, it's a war crime and it's terrorism. Ukraine has nothing to gain by committing war crimes and everything to lose, such as support from their allies and thus, the war.

Targeting civillians is well known to cause civillians to become more supportive of war and so is a bad idea. You target the military and make the war seem like a lot of senseless deaths to civilians who eventually realize they have to pay for it but don't see any gains.