Yes, this.As someone who attended a Chicago Catholic League school that has a history of athletic rivalry with others in the conference, I'll say this: no zip code rules = wider map (to recruit). Besides the usual local kids, my school had kids from NW Indiana, kids from practically every zip code from the inner and outer ring suburbs, to Catholic kids from Pilsen and Bridgeport, plus non-Catholics from not-so-great Chicago neighborhoods looking for an alternative to their local CPS.
The admins' rivals weren't so much the local public school, it was producing a product that was more attractive than the other Catholic high school 20 minutes away who was also bragging that X number kids came from X number of zip codes.
Currently, one of the prime focuses is to succeed athletically where the school president has hired athletic coaches who could delivery the goods. So far it's working. In the past the high school was good at one or two sports in any given season, but now not only is the basketball team winning, but also the football, baseball, soccer and volleyball team both at conference play and at the state level. Unfortunately our cheerleading squad, the gem of the school in past years, has fallen to absolute mediocrity. It'll be a while before they see another national banner.
I would guess Yorkshire Christian is far more selective on who they recruit, whether for sports or academics, to fill out their enrollment in comparison to X or Y public school who can only work with the kids within their district boundaries.
I grew up on the South Side close to Leo, St. Rita, and Mount Carmel. But I went to a different Catholic HS and had classmates from the North Shore down to the south Burbs and even Michigan City. We had kids who were stars on various sports teams who could have gone to Lyons Township, Niles North/West, Homewood-Flossmoor, New Trier, or any other gigantic public school.
Yorkville probably does the same calculus. Also, Yorkville beat my alma mater last week. So it's working.