@Cruzatte pretty well nailed it.
Though for me personally, the challenge wouldn't really be a reason. I do appreciate the challenge, but I wouldn't say it is part of why I use one.
@Magungo1066 is also spot on.
A rifle would have been rare to unheard of here in Connecticut during the time period I am inerested in. Which brings me to Connecticut and the versatility of a smoothbore, specifically in 20 gauge or larger.
I hunt squirrels, turkeys, deer, rabbits as a target of opportunity, and also pheasant. I would hunt grouse and used to,,, but there are so few left I would leave them alone if I found any.
Our game laws are such that if I stuck with a rifle, I would need 2 rifles, and all the stuff that goes with 2 rifles of 2 different calibers, and still would need a smoothbore. Deer can be hunted with a muzzleloading rifle .45 caliber or larger,,, or a 20 gauge or larger shotgun. Small game (squirrels, rabbits, and coyotes) can only be hunted with a muzzleloading rifle .36 caliber or smaller,,,, or a shotgun loaded with shot. Pheasant are a game for loose shot, gauge doesn't matter,,,, but turkeys can not be taken with a muzzleloading rifle and shotgun gauge (muzzleloading or cartridge) is mandated at 20 gauge or larger.
See where this leads?
So for me, where I am, with my personal historical interests and motivations, my budget that won't allow for 3 muzzlers and all that goes with them, and my game regulations, a smoothbore is more than just ideal,,, it is really my only choice.
It helps that I do love it.
Yes, I understand that the strict historical part is a very small to even non-existent factor for many people. For me it is important.