The tolerances(spaces between moving parts) in the AK are loose. There’s lots of room for gunk and dirt to get in there and the gun will still fire and cycle when the trigger is pulled. With loose tolerances, failure to properly clean and lube the weapon won’t hinder it from firing like the M-16 from the Vietnam era.
In addition the AK uses a gas piston technology rather than direct impingement. Both systems use the gas from the recently fired round to load the next round. With the AK the gas is directed to a piston rather than directly at the bolt carrier. This keeps the bolt cleaner and results in less jams. However, it creates additional movement not present in the direct method and therefore sacrifices accuracy.
Gun makers today sets accuracy very high on the “important list” so you cant have these clearings between all the parts because everything will not line up exactly the same between shots. For an AK and at its time this did not matter, as more often than not you were so close to your enemy that you could smell their breath. Today its a different age and you make weapons that are reliably accurate and light weight (AK is a heavy bastard) all these three things naturally contradicts each other.
So while the AK enjoys a legendary reputation, by today’s standards, it’s a pretty crappy weapon…yes, its reliable, but it can barely hit anything over 400m and it is much heavier than it looks.