I don't wonder at all. It is very few. I have taught shotgun to Marines from Quantico, the guys who train the Marines who guard the embassies with M4s. I placed 14th and made the shoot-off at the IPSC Shotgun Championship and compete regularly with a shotgun. I also work with, and train several local LEs on firearms. I was arrested 22 times during High Risk Felony stop training last week. The shotgun is usually the last weapon system I will recommend to a skilled shooter for HD, certainly a last resort for the novice.
Most highly skilled multi-platform shooters suggest the AR15 platform by a pretty decent margin where concealment of the weapon is not an issue. With the surge in PCCs, that is a the space many are starting to suggest as well. After that, it becomes one of evaluating strength, proficiency, environment. I have had folks from 6 to 86 on the AR15 platform do extremely well with it, better than any other platform. Only downside is noise levels inside the house.
Noise is the big issue with the AR inside a home, but I think that's where the 9mm or other pistol caliber AR's are going to become very popular, very quick, especially when you can have a pistol brace on an AR pistol with a 7 inch barrel.
A 7 inch 9mm AR is super fast to swing around and get onto a second target, much faster than a 16 inch Hi Point, Sub 2000, Ruger PC9, Cx4, etc. Those manufacturers need to get on the ball and start offering factory braced pistol version of their carbines or their gonna lose money.
As for the shotgun, if one connects with the target and doesn't dork up the pumping, it's still the most effective short range gun available. The problem is that shotguns can be unwieldy for small/old/weak people, high recoil, low capacity, more susceptible to improper operation causing malfunctions... unless you are an expert a lot can go wrong with a pump action shotgun and semi-auto shotguns can be unreliable.
I would say if a semi auto is reliable, one is better off with that, but even then, the other issues that plague shotguns as home defense guns for unskilled people still remain.
I only have one shotgun, it's an over/under, I get two shots with it before I have to go to something else and personally, I'd rather buy rifles or handguns that hold more rounds and are things I can test handloads with at the range for entertainment.
Shotguns are both niche and cliche guns for home defense. I think too much of the mentality surrounding shotguns comes from movies where people getting shot with a shotgun magically fly backwards because it's so powerful...