I think the thing is that the season arrangements were adopted long before the modern inline muzzle loaders came to promenance.
I would think that the DOW guys working on splitting up archery and ML from rifle never imagined that they would allow high velocity scoped guns in just because they happen to load from the front.
Just last night I hlanced at an article about the new Remington long range ML that uses a primer blank that looks like a shortened 308 and uses a rifle die to deprime and reprime them. The action looks just like a Remington centerfire rifle and I suspect it is.
If I use my Ruger No.1 in 50/110 with an empty case, pour the powder down the barrel and push a lead bullet down, does that make it a muzzle loader?