I would be willing to bet , a lot of it is poor ammo choices.
I remember sitting next to a guy shooting a 16" SCAR 5.56, Fancy expensive scope, expensive bench bags , etc.... after every shot, he would readjust his scope.
Perplexed, I watched him, readjust EVERY time.
20 shots later, he sigh's visibly, and Me, being nosy, I asked "Why" are you adjusting after every shot....
He says he is sighting it in ?!
And he can't get it to group or hit the POA !
I look at the ammo... cheap Winc. M855 ball.
I explained, that ammo will probably never shoot respectable consistent groups smaller than 5 MOA... and he says, his rifle , For what he paid for it, should shoot ALL ammo great.
I tried to explain, that he should consider better ammo, instead of trying to achieve "expected" precision from the Winc. Ball.
Another guy, when the 6.5CM first came out.... was shooting at the other end of the bench line.
Seeing the 6.5CM for the first time, I Spied on his groupings. They were absolute poop.
He would cool down the barrel after every shoot... for about 2 mins.
I had to go watch "why" ?
Getting closer, his scopes rings were half off the mounts.
I mentioned that wasn't "right" and I have the tools to change it easily.
He said his "Gunsmith" assembled it and was sure it was fine.
I said, that will never group right / properly until the rings are correctly mounted.
He says, it will be fine... and continues shooting like poop, every 2 mins.
Ok then...
About a month later, I see him again, This time with the scope mounted properly... groups are GTG.
He come over and tells me, He actually mounted the scope wrong the first time, but was to embarrassed to admit it.
I mention that one because, sometimes peoples pride gets in the way of itself.