It comes down awareness of the Service Academies and numbers of applicants. Some areas like Northern VA /DC area are naturally competitive, there is a strong awareness of Military in general, and USNA in particular. Same for areas with a strong Navy presence --there are a lot of active service members, grads, etc. and all contribute to awareness of the Service Academy. I have heard there can be over 100 candidates from each Congressional District in some of these areas, so the competition is fierce --first to get a Nomination and then to get the appointment from among a MOC slate.
There are other areas of the country with little military (let alone Navy) presence, and little awareness of the the Naval Academy. One of the roles of the BGO is to promote awareness so that we can attract the best and brightest candidates. I'm from a smaller, Midwestern state and I know that the total number of candidates in our state is probably less than the total number of applicants in a single congressional district like Northern Virginia. Our candidates are every bit as qualified as the "more competitive" districts (all that I am aware of have done very well at USNA), but there are a lot less of them, and I suspect much easier for Admissions to accurately select the "best" and most qualified, than having to pick from a more competive pool where the ten persons on the MOC slate are all essentially the same.