The main problem is the lack of scale to spread the R&D costs over. If a part takes $1m to develop, and you only sell a few thousand of them, the part will be i

The main problem is the lack of scale to spread the R&D costs over. If a part takes $1m to develop, and you only sell a few thousand of them, the part will be in the hundreds of dollars regardless of how "cheap" it is to make. QA processes also add a fair amount to the final price as each part might have several hours of individual attention by a technician to make sure it operates perfectly. Even for something as simple as a strut, they might saw every other one they make in two to inspect it for defects as doing so is vastly cheaper than having something fail in launch or orbit.