They're collectible at higher prices because of their relative rarity.
Bosnian 2 rib mags run $30-ish for well-used mags.
Russian blued slab-side run $60-100
Chinese bakelites run in the $80 range
etc etc - not because of how good they are but because of their relative low numbers in the U.S. Bulgarian mags are great, but it's a "normal" import. Since Soviet and Chinese parts can't generally be imported, their perceived value is higher.