This question arises from time to time. Specially, when someone becomes interested in mechanical keyboards for the first time.
The cost of making double shot molding plastic parts is high. It was the preferred method for high quality key caps in the 80s. Other methods to print key cap legends were developed, mainly for cost reduction, like pad printing and laser imprinting. Dye sub infilled applies to PBT but it never becomes popular for mainstream keyboard due to its tendency for warping and because it does not represent a significant cost saving when compared with double shot molding, at high production volume.
Nowadays, the mechanical keyboard community has access to high cost options for keycap making. That includes double shot molding where GMK is the market leader. Its key caps are the best double shot molded ones available second to none. Some other vendors have started to compete with GMK offering Cherry replicas with partial success. Chinese manufacturers also offer PBT double shot key caps at lower cost.
In this context GMK is a German manufacturer that should work from a high wage paying Country making high cost plastic key caps; thus, the final product is as expensive as it could be. The pricing of GMK key caps is not due to market elasticity, but, it is related with its local Finances.
As any niche product GMK key caps are not for all. People that prefer the PBT's texture and its longer longevity compared with ABS have other options now, ePBT, Hammer's, or even the cheap Chinese options. It is a matter of preferences.
GMK inherit (bought) the Cherry original double shot molds, that means that its caps are rightfully an authentic vintage keyboard component re-born. You can always buy any other cap, but with few exceptions, GMK would be the real stuff. Even its tendency to shine is part of that retro feeling. There is nothing close to be typing on caps that you shined by yourself from being new.
The only reason for buying GMK key caps is that you want to type on a piece of technology history. If your concerns are more related with durability (you don't like the shine), or cost, stay away from any GMK stuff.
