My theory on why the AR seems so accurate is two fold: amazingly precise sights that are amazingly easy for the eyes to use. And recoil. The super soft recoil makes it effortless to shoot and shoot and shoot. There is nothing that compares.
Lots of more reasons too. Straight line recoil from barrel to stock. The much-maligned gas impingement system means no steel op rod clanging back and forth. Etc.
I too have wondered if the direct gas impingement system might have something to do with the AR’s extraordinary accuracy. I had a Swedish Ljungman in 6.5 Swedish and it too was extraordinarily accurate and also had the rare direct impingement system.
I was in grad school in the late 80’s when the assault rifle ban hit. I was sitting pretty I thought. I had over 200 guns including a large number of the most desirable ones. I had three brand new H-Bars still in the box each with an included .22 LR conversion kit.
I got pretty hard up for money as it took me much longer to get through than I first thought it would. I would hit gun shows with my guns and was disgusted at most dealers. They would have a well used AR-15 priced at $2500 and would not give me $700 for a new H-Bar. Same thing with high capacity mags. They wanted $90 for theirs and would offer me $15 for a brand new Smith & Wesson 15 rounder which would also fit several guns beside the S&W.
When I finally got out of grad school, I had around a dozen guns. I then had to retire on disability and have not rebuilt my collection but one day I will.