Think about what DavidAnderson said. There's more truth to that than shows on the surface.
There are quite a few 18u teams in Ohio, but the TOP level teams will have a roster full of already-signed college recruits. The thing is, other than staying sharp for college, they have nothing to prove. They no longer need to showcase their skills to college coaches, because they are already signed. Lots of these girls won't play full time, because of workouts, jobs, etc. Getting ready for college - both academically and athletically is the priority. Traveling every weekend usually doesn't fit that agenda. 18u is very competitive, but just a more relaxed mindset. Putting a team together every weekend can be a challenge.
IMO, the 16u teams really have more to prove. Compuware, Stingrays, Sluggerfest, etc. - that's where you'll see these teams battling for playing late on Sunday.