Eric Barker from a June 2014 Time article:
Two factors appeared to exercise the greatest influence on personal relationships: the location of the apartments and the distances between them. The most important factor in determining who would be emotionally close to whom was the distance between their apartments.
What underlies this? Obviously, you have to meet, but there’s something else going on: repeated exposure.
As marketers know very well (and anyone looking for love should learn about marketing), repeated exposure makes us like almost anything.