It's not just football. Sheridan struggled to put together a soccer team last year, and it looks like they might not be able field one this year. To me, it's a generational thing. With more and more athletes choosing to focus on one sport exclusively, it is becoming harder for, especially small schools, to field teams in every sport.
Between specialization and lack of interest in participating, I don't really know what the answer is. Outside of allowing co-ops, I'm not sure what the IHSAA can do to solve this unique problem.
To your question about more schools, I'd be shocked if Tri-Central has a full team this year, just based on what happened last season. Greenwood Christian already backed out of their season, as well.