Pardon the poor grammar, but:
- because even if all you keep is the body and grill of a mic, it still cheaper than having custom metal work done. If the body and grill work, you can put in whatever guts that fit that you want . Even the supper crapulent mxl 2001 was the basis for the well-known Royer mod. Scott Dorsey talked about how part of the reason that the stock MXL 2001 sucks so much is because the capsule isn't powered properly, which is a large part of what the Royer mod corrects (and what is different in the Mojave mics (which IIRC, use ADK capsules).
- because, a good tech will change everything that matters without the kind of markup you will see in a retail product.
- because companies like Telefunken, Shinybox, Charter Oak, and Mojave audio, among others, do exactly that and incorporate a cost increase that suits them, plus all of the steps of the retail market in between.