Aren't large circuits simply born out of the instructor giving the student a bit more space and therfore time to sort it all out, especially when reconfiguring on base before slicing through the extended centreline.Some people then just don't get shown how to make the circuits smaller once they get it.
People do seem to fit into the pattern of the field. Fields like Rochester usually fly nice tidy tight circuits and Biggin always seem to have monster circuits. Gliding sites like to do thier circuits within the field boundary.
I learned at Civvy club on an RAF field. It was not uncommon to go from being number 1 in a square circuit to number 4 as the three bulldogs behind you all cut in on their constant aspect approach and I never once had to go around. Their approaches certainly took less time.