Most people with lower numbers are not well informed/get poor advising and apply narrowly or to schools that are too competitive for them. Or apply too late. I have seen it again and again. There are several users here that are reapplicants or that have not had any luck so far this year; I ask them what schools they have applied to. 9 times out of 10 they are not applying broadly or wisely enough. I would like to point to the underdog Braun as an example of how one with less competitive numbers should apply- she applied to all 3 new schools, plus the lower tier schools like PNWU and LMU. Two unsuccessful underdogs from last year meanwhile, Felix and GMCGuitar, hardly applied to any of the less competitive schools.
I will qualify that there was another unsuccessful UD last year with around 3.6/3.4/22 who did apply broadly, but only received 1 interview then rejection. But they had a 6 on Bio. I contend that if you have a 23 with Bio not less than 7, an OK GPA, and apply early/broadly/wisely you stand a solid chance.
The average applicant only applies to 7-8 schools because many receive poor advising and think all DO schools are around equal in competitiveness. But they simply are not, and many people short themselves by not applying to those lower tier schools I mentioned earlier.