1) No one expected them to be so weak and miserable. Note that every western analyst gave it at most 3 days (some might have said 7, but no one said more) before Kyiv would fall. Note also that even over a month into the invasion, and it making no progress, the narrative in western circles was that it was a result of a temporary logistics problem and/or using conscripts as cannon fodder. The professionals would come anytime soon and then Kyiv would be taken.

2) Nukes.

3) Even though the Russian military appears increasingly incompetent, they are still capable of creating immense damage and destruction.