You are referring to some of the highest quality sets, like GMK, and some SP that are also not cheap. But, there are low cost sets, that are not even considered to be offered in sites like this, for example some lasered thin ABS.
In general the high cost of manufacturing of quality keycaps is what made them economically unfeasible with the cost reduction trend of input devices. It happens the same to the switches technologies that moved from complex discrete mechanical designs like cherry, to low cost mechanisms that use a rubber mat with domes and metal bubbles to replace the discrete switch technology with great savings.
In summary, the keyboard enthusiasts, by definition, are willing to pay hefty prices for high quality components, that the rest of the people consider outrageous due to the cheapo option in keyboards.
