There shitty reputation was a result of some issues in the very first production run that was first shipped to vietnam. The first flaw was in the barrel. The originals didn't have chrome lined barrels so they were prone to rust. They weren't shipped out with cleaning kits because it was thought that they required little or no maintenance. The powder in some of the early ammo was not appropriate, but since there was a bunch of the shit lying around, the ammo was used with the wrong powder which made left the barrels a shitty mess (and as I said, no cleaning kits supplied.)

Overall, it's a very good rifle, but it does require cleaning from time to time. And when they're maintained properly, they're light years better than the AK.

The AK is popular because it's cheap and yields tolerable results.