Personally I think it has to do with population density and maximum range, north of that line where the glacier plowed everything over, Ohio is pretty small flat state, and rifle cartridges can go 700+ yards, where as a shotgun slug goes 150 yds with a tailwind on a good day. longer wide open ranges = more likely to hit a house, car or person. I wouldnt want to be downrange of that.
Whereas, I'm from southeast Ohio, and it is nothing but hills and valleys, I dont see any reason rifles couldnt work as well as a shotgun.
My guess is someone decided that even though we can have varying bag limits per county, we cant have varying weapons laws. Id say it just makes it easier to enforce.
I hunt with a revolver anyway, so it really doesnt make any difference to me.