Because you don't overrun a nuclear state with weapons, but with influence and the true promise of scaling up.
The truth is, Europeans know that if Ukraine falls nothing will happen to Europeans. There is no existential threat. There has been no national mobilization of industry to support Ukraine's war efforts.
The entire western world over the last 3 years has left Ukraine with a 10-1 artillery disadvantage. It's just not a serious concern for people.