ARs are common because the US military and NATO use them.
Same reason sig Sauer pistols are popular.
Popular is not the same as "superior".
Once the US moves off the AR platform, so will all the gun nuts.
I say this as a former armorer who got to see why ARs might not be the best choice.
True, but primarily, because NATO wants them in a certain spec.
Again, once the US military switche from it, then so will everyone's opinion.