Manufacturing costs and price the manufacturer charges are not the same. I know from multiple discussions with designers that it's a delicate balance that needs to be struck with kitting, so price for the consumer is good, MOQs are reachable and vendors make enough profit that it's worth it for them. Adding keys that almost no one needs just makes the sets less attractive to the stakeholders. That's why Mac support keys are usually a separate kit (if there is support at all) even though those 5 keys or so could have been put into a base kit / mod kit