At least some countries (smaller ones) have good students and good
LORs concentrated at one (or two) universities and thus applicants face congestion regarding
LORs (they have worked with the same profs). They split up the places where they want to apply and thus they get full backing from their institutional and professors. That could lead to them not applying to the same places. I'm not sure this is all that common but at least it sounds plausible in my country.
Regarding the fee being restrictive, IMHO, I think most applicants from low-middle income countries do not apply directly from the undergrad so they usually have some work experience(RA or teaching, CB etc) and $$ to pay for the marginal application. They also have significant uncertainty which thus makes diversification more attractive. Plus US dollars aren't worth all that much these days anyway...
