Plus, of course, each European country has to support their own defense industry, so each one of them needs to have their own howitzer/tank/whatever and they can't agree on common approach that would actually allow for the economy of scale.
https://time.com/archive/6731121/how-clinton-decided-on-nato...
We will see whether the new realities of the war in Ukraine and Trump's approach to Europe will substantially change that.
The whole economic and societal tensions in the west make things tougher...