As an American living in Germany for a few years now, this is something I really struggle with.
In short, it's because Europeans are content with lower wages.
I am in a "high-demand" job as an electrical engineer at a publicly traded medical company, and getting less than €65k. This is absolutely absurd in my opinion, but in discussions with friends/colleagues they feel it's overall typical.
One colleague was in shock when I said I expect to break €100k within the next few years (Sr level)... But was also completely unaware of any basic public company financials (average value of employee is ~$350k), or salaries in our USA office (~$160k).
Unfortunately, my value is not related to anything other than my cost of replacement--since my neighbor thinks €65k is acceptable, that's what I get.
Company performance, employee benefits, healthcare, taxes, etc do play a role.... But it's nowhere near the salary gap.
Help me spread the word OP. Tell all your friends. Start demanding more. Mercedes recently announced all employees would get raises matching inflation. It's a good start but honestly we need to recognize this as the bare minimum, not like they are heroic and progressive.
Ps: Hope nobody minds me dropping numbers. I have no insecurities and don't care, but believe it can be a good help for the discussion.