The better sports program=the more money for the school.
I went to a school that was ranked 1st D2 Sports Program in HS while I was attending. 80% of the students played some kind of sport. What you start seeing in higher levels in HS was that practices tended to focus on the teamwork; personal skills, you were expected to practice on your own. Thats like 5+hours a day worth of practice.
Most big sports such as football, basketball, track and field, baseball, and other less known sports such as wrestling, waterpolo, etc. They determine on the school competition to help them get scholarships and attention. For them school season is the most important.
With hockey, soccer, swimming, some wrestling (freestyle and greco), etc. Clubs were often more important than schools for these sports, however the school season was just a time to show the schools what you were made of.