it's all about logistics and weapons
https://www.csis.org/analysis/russias-ill-fated-invasion-ukraine-lessons-modern-warfare
evertheless, the Russian military faced numerous challenges in conducting its air campaign.
First, the Russian air force failed to achieve air superiority against a Ukrainian military with notable air defense capabilities, such as Stinger man-portable air-defense systems, S-300 surface-to-air missile systems, and other systems—thanks, in part, to Western aid. The success of Ukrainian air defenses deterred Russian aircraft from freely operating over most of Ukrainian-controlled territory. This meant that one of Russia’s primary ways to strike deep into Ukraine was through cruise missiles launched from Russia, Belarus, and maritime vessels in the Black Sea.
Second, the Russian air force faced recurring logistics challenges, including running low on stocks of long-range, precision-guided munitions. Three weeks into the war, for example, the Russian air force began to run low on precision-guided munitions, such as laser- and satellite-guided bombs, which caused the Russians to use a growing number of unguided artillery shells, rockets, and missiles from the ground forces.18 When it came to weapons systems such as the Iskander-M short-range ballistic missile system, the Russian military was also hesitant to expend a portion of its stockpile, which it needed for defense against the North Atlantic Treaty Organization (NATO) and other threats.19 In addition, dozens of Russian UAVs, such as the Orlan-10, Orlan-20, Orlan-30, Eleron-3, and Forpost, were shot down on the battlefield or subject to electronic jamming.20 These challenges were exacerbated by t