Shitty logistics and tactics.
It was so bad in the start to the point top of the line pantsirs were stuck in the Ukrainian mud. Kilometer long lines of military convoys which were getting ripped apart by ATGM teams and drones. Invading Ukraine with 150k troops and being hesitant from going in full steam.
Russians were dumb af to believe the invasion would be like Crimea operation of 2014 where they would be treated as liberators.
Please recall, they took the airport and the nuclear power plant.
I do not buy your explanation.