Maneuverability
We’re not hunting geese with short barrels. The short-barreled shotgun (SBS) is meant for tactical offense and efficient self-defense. The short barrel gives you greater maneuverability inside buildings. If you know you will be outside, and not in confined spaces, then a full-sized gun will work fine.
Full stock
Many of the shotguns that try to stay compact often shorten their stocks. These are often called PGOs (pistol grip only). They’re not technically shotguns, according to the ATF. They are firearms. And they are hard to control because they don’t have stocks. The first shot is easy, but muzzle flip is absurd. A full-sized stock with a short barrel is much easier to control.
Easier to load
Bullpups have a devoted fan base. Guns like the Kel-Tec KSG have incredible capacity, but loading them may be a bit awkward as the rounds have to go in below the stock. The method can be learned, but it requires practice.
Familiar manual of arms.
While we’re talking about the way the gun operates, I’d add that there are advantaged to going with what you know. I’m running a Remington 870 because I know the 870. I grew up hunting with one. Before I gave Uncle Sam some money he didn’t really deserve to allow me to cut of the barrel on this one, I used it as my go-to home defense gun. Go with what you know.
Better balance
A fully loaded KSG is a beast. Dumping 14 rounds of high-brass buckshot is one of the most heady shotgun shooting experiences you can have. Most of the bullpup models that have taken off are either double barreled or have two magazine tubes.
That’s a serious benefit, but the gun can get cumbersome. My 870 is lighter, easier to swing, and the whole package is very well balanced. Because it is thin, it is also easier to conceal.
The point of the SBS is its ease of use. Anything that detracts from that is nothing but a distraction.