I think that Russia may have a two-prong strategy: either make sure Ukraine is not joining NATO, or make sure that Ukraine that joins NATO is completely wrecked.
In the alternative reality, where Ukraine promises tomorrow not to join NATO (ever), the Russian targets for this war may be considered achieved, and everyone could simply go home, probably throwing in a couple billions deal for Ukraine recovery. This would be the best outcome for everyone. But this will not happen tomorrow.
If this won't happen at all, the Russians can always wreck Ukraine later, and this is where their air force may play part.
In short, I think the Russians are showing some restraint, for now, to make sure the quick outcome still can happen.