The research output from UK and Germany are disproportionately large compared to other European countries (which you can see based on the number of Marie Curie or ERC grants awarded/capita to people in those countries versus others) and in general. They are research powerhouses in general, and also specifically in matter modeling research (consider the countries of origin for software like MOLPRO, CFOUR, NECI, HANDE, etc.).
There's currently only 1 user from UK in our list of top 24 users by reputation, and 0 from Germany (the following list is not too different if consider "most active" users by number of total posts instead):
|11||taciteloquence||USA / Taiwan|
|15||Etienne Palos||Mexico / USA|
|18||Anyon||undisclosed but possibly USA|
|22||Kevin J. May||USA|
I stopped there because I don't know where megamance is located, but I'll say that:
- The next highest-rep user who is certainly in UK is Phil Hasnip (#31) and the top user in Germany is wzkchem5 (#26).
Why might this be? Our first instinct might be to think it's a cultural thing, but:
- the #1 user on StackOverflow is in UK (as well as #6,#8,#9, and #12),
- the #1 user on Quantum Computing SE is in UK
- the #1 user on AskUbuntu is in UK
- the #1 user on Physics.SE is in UK
- the #1 user on Electrical Engineering SE is in UK
- the #1 user on MathOverflow is in UK
- probably the trend continues, but I only looked at the sites with 100,000+ questions (and I knew this about Quantum Computing SE since I'm active there).
What might be the reason for this? The good news is that this data indicates that this site has a huge potential to grow from where it is right now!