I guess you weren’t around to see tons and tons of scopes mounted on carrying handles in the 1970s, or scopes mounted on home-made flattops which only required cutting off the carrying handle, which is not integral to the receiver but simply a cast on appendage.
The point being, an ARs upper receiver is inherently stiff and ready for very accurate iron or glass sights.
For an AK or a FAL, you have to do some pretty serious aftermarket purchases and work to put on a solid optic. It’s just inherent in the design of the rifles with dust covers.
I think I spent about $50 a few years ago for my dust cover and installed it in about 20 minutes. I've broken optics and charging handles but I've never had a problem with the dust cover. (Sadly the TAPCO piece in the second article is no longer available.)
Not having an AK I can't speak to what kind of work it takes to make one of those accept a dust cover, but for the FAL it "just works."