It's not even just that it's expensive: if you look at a cable that's full-everything including top-rating for power delivery, it's a pretty thick inflexible thing and not at all what you want for e.g. a mouse or a keyboard or whatever.
This isn't even new. Even USB 3.0 (the first gen, later rebranded as USB 3.1) micro-B to A cable, which has been around for at least 10 years at this point, is already not good for mouse. Nor is my USB-C 2.0 with 60W PD cable.