Per the NCHSAA it's all about reducing travel costs and limiting split conferences as much as possible, which makes sense. All 400 schools have their "natural/bitter" rivals(which may or may not be in all sports; for example there are some fierce girls volleyball rivalries between national-level programs that probably don't carry over to football. Don't look for the NCHSAA to try and accommodate any "rivalries" as we fans define them; just not practical.