Because you are designing and producing a one-off items. Basically, you are engineering a tool which allows you to shoot molten plastic at high pressure into tiny cavities, with tolerances smaller than a tenth of a millimeter for the end product. That's not
at all trivial and therefore unaffordable, unless you are building molds which will be used to create tens, if not hundreds of thousands of copies.
The cheap option is to reuse an existing mold, mostly by asking a manufacturer to create keycaps in an existing profile, but in a color of your choice. That's what almost everyone in the keyboard industry does.
I agree with the OP. Either they have to sell tens of thousands of this keyboard, or it is going to be priced in the high-hundreds or even low thousands of $.
