Note that in the USSR proper, only the magazines ended up orange (made of glass-reinforced phenolic resin called AG-4). Even the pistol grip was a darker brown shade.

(I guess it's a different type of resin, also reinforced but with shorter fibers (look like specks, whereas in magazines you clearly see the long, wavy, hair-like glass fibers), and in a darker shade. Since it's much thicker than the magazine walls, it can be simpler and cheaper, closer to the OG Bakelite like telephones.

AFAIK it's the other socialist or USSR-aligned countries that experimented more with making various furniture from resin. Soviet guns that have a lot of this resin are often prototypes — it's the thermoset polymer that was available to designers, so similar to today's 3D printing. The Soviet military only transitioned to all-polymer (handguard and stock) in the 1980s, with the AK-74M — and they didn't use reinforced Bakelite anymore, but a type of polyamide instead. I guess they weren't content with AG-4 furniture's durability.

I also want to point out that you make it sound like using this plastic is the result of the USSR being technologically limited... But this is literally early 1960s. It's pretty cutting edge. And successful: AG-4 mags last forever, essentially don't deteriorate, and are strong AF. Remember that the M-16, introduced in the late 1960s, was considered weird and space age because it used polymers.