The problem is that, even if they want to (which they do and european defense stocks are seeing big gains recently), their readiness and ability to manufacture at scale isn't there and will take rehauled investments, processes and -- more importantly -- time. Time that they don't have for current issues like Ukraine.
This is an example of the many examples of the negatives of an overly globalized and horizontal world. If and when relationships change, you lose autonomy. It's why it was an absolute error to outsource the packaging of chips back in the day because now the Tawain/Asian area of the world owns that unfair advantage while we are trying desperately to get caught back up and control our destiny to a degree in-house.
The flip side is, all the efficiency gains and scale you got in the peacetime years for globalization couldn't be nearly matched with the entrenchment and insularity of a more protectionist and less open system.