It’s a combination of poor training, terrible battle planning and a dire lack of manpower. At the start of the war, the Russian Ground Forces had 300,000 men in uniform, including conscripts. Ukraine had up to 250,000 men at that point including the territorial defense units.The Russians are really losing the war now. According to the foreign affairs chief of the WSJ, a new poll shows support for the war in Russia has dropped to 48%.
The question is why are they still losing? If it's a matter of manpower and policy (such as limiting strikes on Ukrainian targets) they can turn it around. If they are outgunned by superior NATO technology they are really in trouble.
Against a determined Ukranian defense, Russia needed to amass at least 750,000 to ensure a quick and decisive victory. But they didn’t take Ukranian capabilities seriously not did they understand the extent of anti-Russian sentiment in Ukraine.
They are now up against a fully mobilized nation state with over 700,000 men (and growing) in uniform buttressed by the largest military alliance in the world. Russia needed to begin mobilization back in April, but Putin the chronic procrastinator that he has always been, preferred to kick the can down the road. Well, surprise, surprise : he just ran out of road.