Interesting observation. My wife and I have camped at (almost) every State Park and State Recreation in Indiana over the last few years. We have 4 more parks to go and we will have stayed at every one in Indiana (State... not private)...
Anyway, an interesting observation. At the State Parks in Northern Indiana (especially the North East) -- there is a very high proportion of pop-up campers. In the Central section of Indiana there seems to be a 1 for 1 mix: pop-up, TT, 5er, MH. (But TT's and 5er's are still more dominate). In the Southern part of the state, 5er's and horse trailers are the dominate RV in the state parks. Very few pop-ups in the Southern part of the state (that we've seen) at State Parks. It was very noticeable this year. So I think it's REALLY a geographical --- oddity.
You would think that Northern Indiana would have more motor homes, trailers and 5ers because this is the Meca of RV manufacturing. But PUPs rule! In the South, you would think the opposite. But not so.
I'm still baffled at this observation.
Not sure what's going on with the dealers, but when I think about the various dealers in my geographical area, you are right, there's not very many pop-ups. So I still think its a geographical "law of supply and demand". If the demand was more in your area, you better believe the dealer lots would be full!