I'm not sure I understand the intent of your questions? Feel free to clarify if I've missed your point.
I was not implying there isn't open enrollment to those schools. Rather, the opportunity to open enroll there, probably isn't as great as it would be for schools in a metro area.
My overall point was, rural 1A schools will not have the number of students transitioning into the district, and likely not have comparably open enrollment options when compared to a 1A private in a metro like a Des Moines, Sioux City, CR or IC area. In other words, there are likely more jobs and family opportunities moving to a Des Moines than a small town like a Sigourney or whatever rural 1A/2A school you'd like to use as an example.
I simply picked a handful of rural 1A schools as an example. Feel free to pick any rural 1A school (Winfield Mt. Union, Waco, Pekin (Packwood), Cardinal-Eldon, etc.) and use them instead.