For a number of years, Ann Arbor Pioneer dominated girls track in Michigan (14 state titles in 28 years; never lower than fourth). For most of that time, Pioneer was one of the top five largest high schools in Michigan, with 2800-3000 students. However, they normally had about 40-45 girls on their team. The commitment level was the same as F-M. They would run XC in the fall (very few of the track athletes did another sport) and then take a short break (1-2 weeks). They would then run a full indoor season (9-10 meets) and go right into outdoor season. After the high school season, they would run the USATF/AAU summer meets and finish in late July. After a couple of weeks off, they would start XC again.
If you weren't willing to commit to being on the team year round, you didn't come out. Students knew that coming into high school that you had to make that commitment. Most high schools that size get at least 100-120 kids per gender out for track. If you don't want to be that committed and just run outdoor track, no big deal. The more dedicated kids make the varsity, qualify for state, etc., but a kid could still participate in track without the all-in mentality. Schools like F-M and AA Pioneer aren't like that. It also helps the coaches to focus on the committed athletes and not worry about dealing with a couple of 6:15 milers who have shin splints.
Running that type of program, a coach may miss out on a kid who may come out just to try it and realize they have talent. Overall, however, the kids that are real serious will gravitate toward that type of program. It's just like a kid that will play AAU basketball in the spring, summer, and fall to be successful in high school basketball. There are just less running teams who do that compared to football, basketball, etc.
Getting the kids to buy in to what you are coaching is, in my opinion, the biggest factor in raising a program to championship levels. It doesn't matter how much talent you have on the team or how good of a technical coach you are. If the athletes don't buy into and commit to your program, they will have limited success.