I see that question posed quite often. Gun control advocates want an answer; what they get is "because it's my right". That answer IS correct, but since they're generally not gun owners, it's an expendable right in their opinion. We need to be able to articulate why many are drawn to the AR platform, or "black guns" in a way that makes sense to them.
I have thought about this a lot. I think I might have an answer.
I'm 53. As a young person, all guns I recall were wooden stocked. Revolvers had wood grips. Wood brings out thoughts of "use afield". Plus, these are the guns that were my introduction to shooting sports. When I think of a "cool gun" - even today - it would be something like a model 1894 lever gun. When I trained on the m-16 in the Air Force, I thought it was ugly and utilitarian; nothing that interested me as "art of the firearm".
Now let's fast forward to today's new gun owners. Let's look into THEIR introduction to the shooting sports. In my opinion, I think many folks first introduction to firearms in through military service. We've been at war now for about 12 years straight. There's many younger folks whose first introduction to the shooting sports was the AR platform. As far as handguns, the m-92 hi capacity 9mm. To them, this IS the "art of the firearm". To them, high cap "black guns" are the epitome of a "defensive firearm"
I'm sure this extends back to vietnam era veterans also, but older guys probably have a wider view of what constitutes a "defensive firearm".
Because my training throws back to a "previous generation", I DO find a shotgun to be an ideal home defense weapon. Younger folks probably gravitate to the AR for home defense because it's what they were trained on, what they're comfortable with, and what works.
Bottom line, I think your introduction and training in firearms probably drives your choices on WHY you select a particular weapon to own. I think this explains why there's such a gravitation, especially among younger gun owners, to the " black gun". They have no prejudice against polymer or pistol grips. Parkerizing and picatinny rails are normal, right? Wood gets dinged up, blueing rusts, and iron sights are antiquated in their minds. So why not get an AR?
One real irony of the gun- grabbers current attack on "assault weapons" is that they are in large part trying to disarm the very people who have fought for our country in the last decade or so. It's so ironic that these veterans could be trusted to defend the rest of the population's rights, only to find their own rights under attack by the very people they fought to defend. JMO, Steve