[ant6n]

It’s easier to have very specialized friends of they are geographically far away.

[hrimfaxi]

I don't see what distance has to do with it. I had a number of specialized friends in close proximity at university.

[trenchpilgrim]

Presumably because they all traveled there for a temporary part of their lives. And after university, they presumably scattered to the places where they built their careers and families.

[esseph]

"at university"

Clearly proximity is involved