"Worldwide popularity" is myth. Most nations worldwide don't allow open possession of firearms by civilians like we do, uprisings and coups would be even more common than they are. Government controlledl access to firearms practically requires being in the armed forces, and having a paycheck helps ensure loyalty.
What firearm that government chooses to distribute has nothing to do with popularity,a lot more political polarity. The AK is a weapon distributed by the Soviets and their related allies, and when given to actual freedom loving patriots, used to overthrow an monarchy and institute what quickly becomes a People's Republic. It's a nasty, notorious fact a lot of freedom fighters are quickly executed in the dawning days of a new regime to consolidate a Communist victory.
Once properly aligned, the new government accepts shipments of even newer models of AK's, and may even get it's own factory. Hence, the widely varying patterns and standards that make even interchangeable mags problematic.
Note, none of what happens is due to marketing or consumer demand choosing a "superior" weapons platform. The 50 year track record of the AK is to overthrow governments and institute even more oppressive ones. None of that is due to any superior design characteristics other than being the only gun provided.
"Popular" is a stretch - handing out AK's like candy at a orphan's ranch to third world citizens with no training and little education is all about empowerment, not an educated discretionary choice when perusing the market bazaar for a HD/zombie/SHTF recreational firearm.
AK's actually SELL for money in the US because they can, are cheap, and that's all the discretion a buyer needs to have, too. When free world defense experts can exercise choice, the AK is notoriously absent in the lineup. Choices become competitive, and the experts don't choose AK's.
I note the Saiga shotgun had gas residue buildup enough at 1,000+ rounds to cause the piston to stick when disassembling it. Point made, they are not impervious to neglect. NO gun is, it's marketing hype disguised as a "word of mouth" recommendation.