Since it's introduction, there's been more than 20 million soldiers, sailors, airmen, and Marines taught to use one. That put more Americans out there with a base of knowledge on AR's than any other firearm in American history.
What they knew for a fact was that it disassembled easily, and the individual could work on one a lot more than any other gun they ever had. It's not uncommon in the military to see a lower with no LPK in it being cleaned. It's not user maintenance and prohibited, when did that ever stop everyone? Plus, you do specifically tear down the bolt, and get familiar with a lot of it.
When the A3 was introduced, it got my attention, most of us serving even part time recognized there would be a lot of versatility in the design. It would be possible to clamp any sight we wanted on it, and voila, the service immediately did start putting red dots there. No longer would long belled Fudd scopes be the only awkward solution.
The AWB only added fuel to the fire. You can't tell American's they can't have something for no good reason. And there was no good reason. Chafing under the restriction accomplished exactly the opposite of what gun banners wanted. Once hi cap mags and pistol grip mags were made proper again, folks who wanted one because they had reasoned they wouldn't be told different bought them. And they were getting good ones, too, largely milspec quality with few corners cut, by and large. No cheap imports, and the low quality players were instantly revealed through a new phenomenon - the Internet.
A lot of AR growth is directly tied to the rise in use of the Internet. People who had no idea, or who had been fed a lot of wrong ones, even total BS, could surf around and find their curiousity either satisfied, or worse, piqued by the contrasting opinion. And rather than be stuck with Elmer's opinion at a gunshop, they could get straight, factual data from knowledgeable, experienced users.
They discovered the design wasn't the maniacally evil stepchild of crazed survivalists being carried broken down in M60 barrel bags. It was actually nice to shoot, and their fragile manhood wouldn't be dissed by the looks. It was certified mankilling military issue.
There was still the caliber question, Americans tend to think ammo should anchor any target or opponent DRT. And in the early 00's, new calibers kept coming out. Those made it legal to use hunting, which is real shooting at live targets, not paper punching on some Range Nazi's home turf. American's like to go out in the woods totally unsupervised and blast away at things, destroying them. Can't do that on ranges that don't allow full magazines, don't offer 180* downrange facilities, require structured rules like leave it on the table or mat and NEVER touch it, much less OMG, shoot while actually MOVING! (The horror, the horror.)
BUT, you sure have to do that on a three gun match. Once the 5.56 was accepted there, it showed what most knew - the AR15 got the job done better than the C&R's everyone was restricted to use at the First SOF in Columbia.
Since the decentralizing of American manufacturing to smaller shops, many more suppliers saw market niches they could fill. They did, bidding for smaller lots of government contracts, and selling direct on the Internet. Again, the typical B&M storefront with increasingly hidebound liberal management who wouldn't go further than sell traditional firearms fell out of favor. People bought over the net and shipped to their own door. Bluntly, screw them, we are not going to wait for Elmer to get around to carrying a low demand specialty part, especially when he's been obvious about disliking the design, and will only order from mainstream distributors. Not even going to push that with him, a few keystrokes and it's here THIS WEEK, not next month.
I've had one - 1 - transaction for a part in a storefront in my build, the lower, as required, thru the FFL. Every other piece, literally, lock, stock, and barrel, has been delivered by a parcel service to my front door. What's not to like about assembling an AR EXACTLY the way I want (and can afford) on my budget and terms? I can research, question, get answers, find out what works vs. what's hypemarketed, and think at a pace that becomes increasingly knowledgeable - rather than hustled in a Boxmart or gunshop that structures the discussion and impending sale with only what they want you to know?
Darned AR's are selling like hotcakes because the Fudds can't stop it. Jim Zumbo and the gunwriter bolt gunners are getting left in the dust of yesteryear because they are all part of the traditionalist pro/anti gunner syndrome, and won't overcome their bias against them. They no longer control the flow of information, forums and blogs do - the Internet again. If anything, read the American Rifle articles on the 6.8SPC - Bryce Townsley con, as any old bolt gunner would be, churning over dated facts and a clueless mindset, and Bill Wilson, who actually hunts with what he sells, leading edge participant and knowledgeable in actual market trends, business, and (wait for it) real gun knowledge of shooting live targets.
The huge increase in the AR is directly tied to the A3 upper and the Internet - the shooter benefits with both, and gets straight facts that see through the manipulation and marketing controlled by the status quo. It's affected more than newspaper sales. We're quietly having our own revolution here, shaking off the chains of distribution systems and controlled information. That really has some old school money makers concerned. They very well would make a deal with the devil to preserve the status quo they favor, don't trust them one bit.