tbh it's a wonder there's as much variety as there is in airsoft, but there are plenty of guns that aren't catered to.
the bren is a good example (although afaik there is a zb26 out there) and the sks.
the makarov at least has a decent offering in the WE version, doesn't like the cold but with a little tweaking it's a very passable gat as a holster-filler.
not just guns either, optics, especially russian ones (that aren't a PSO) are quite poorly covered with only a couple of decent clones for the likes of the PK-A or Kobra. fortunately this is balanced by the real ones being both available and not insanely expensive as RS optics go.
i think the problem is it's just so easy to do AR variants, mill out a worn-out mould to a chunkier style, change the handguard/stock and bam you have a "new" gun (psst, it's still an AR....)
also how has nobody done a G11? that must surely be one of the easiest wacky aeg's you could make.....