So what's more likely, Ukrainians are good at hiding aircraft, or Russians suck at bombing airports?
I really don't know. I think the Ukrainians air force got at least some basics in camouflage and seeing the results and hits of the past months I certainly believe the Russians can bomb effectively.
Maybe (I'am not an expert in that kind of operations) the Ukr Air Force is operating on non paved runways or highway strips. What I know about MiG-29s is that they have a rugged landing gear with mudguards on the front landing gear and that the main air intake is closed during take of and landing and the air is sucked in from above.
The Su-24 has a rugged landing gear as well and mudguards. How the air intakes handle unpaved runways I don't know. About the Su-25, there several pictures of them taking off and landing at unpaved runways.
If they do this I don't know but it could be an explanation. A single Su-25 hiding in a treeline and taking off from a stretch of highway or grass strip is way more difficult to find than an fixed airfield. Logistically it must be a nightmare because you have to supply fuel, aircraft bombs, ground servicing equipment to every corner of the country.