this article is a very good summary of what happened https://americanaffairsjournal.org/2021/08/the-value-of-nothing-capital-versus-growth/

I think it’s mainly due to outsourcing. They de-industrialized themselves and can’t even manufacture enough to supply their own imperialist armies. Europeans have no idea how lucky they are that Russians have so much restraint. If Russia wanted to go all the way to Berlin again, they could and without much effort.