Hunting regulations seldom make sense.
For example, my home state legalized smokeless this year for muzzleloaders (which can really improve velocity), however when asked about 40 caliber bullets (which are illegal) an offical of the Illinois DNR gave me this answer:
The same projectile specifications (.44 caliber) apply to both shotguns and muzzleloaders. While that regulation predates my tenure here, I'm guessing that the reason it was put into place in the beginning was an attempt to keep projectile size fairly large and limit velocity (i.e., and therefore distance). Part of the same package as prohibiting use of high powered rifles.
Another interesting fact about Illinois regs, a 45 caliber muzzleloader shooting a round ball is legal. The roundball for a 45 measures .440 and weighs 128 grains. The smallest 40 caliber bullet is 150 I think.
I'm sure every state has dumb regs written by folks who don't know a muzzle from a breech. These are just a sample of Illinois dumb ones.