Having a goal to destroy airplanes, Russia wanted to gain complete dominion over the sky, so that it would then be possible to take Kyiv at lightning speed considering deliver military personnel, equipment, and ammunition by airplanes to the nearest airfields.
Russia never stated any goal of taking over Kivv, and its far too risky to bring things by plane instead of train. They may have not bombed the airports because they wanted to use them but it could also be that they didn't want to bomb them simply not to cause unnecessary damage, after all they didn't launch a full scale invasion and they couldn't take a city of millions with not even 50k troops, plus considering that they took up defensive positions in the locales surrounding Kivv but didn't completely encircle it, maybe 60%, it seems very likely that it was directed at cutting off reinforcements to Mariupol by making the AFU fixated on defending Kivv, especially when you consider that they pulled out when Mariupol was 90+% taken and the 36th and Azov battalions had almost completely retreated into Azovstal.