Actually, I’ve heard that a whole lot of operators stopped using piston ARs a few years ago and switched back to DI rifles. A well built DI AR-15 will work long and hard before needing cleaning, I’ve read that a Bravo Company bolt and carrier group can go thousands rounds before cleaning.
What happened is that they came out with many new coatings for the bolts and carriers, like Boron Nickel, that drastically improved the cleanliness and reliably of the weapon.