Unfortunately that's not usually a good enough motivation for most companies. To be clear, I'm not arguing that I don't think it would be a good thing for them

Unfortunately that's not usually a good enough motivation for most companies. To be clear, I'm not arguing that I don't think it would be a good thing for them to release the code (I most certainly would welcome a fully open source rpi), I've just been confronted to this mindset a lot at work. Closed source is the default, releasing anything publicly means going through many hoops and levels of hierarchy. If there's no obvious benefit for the company and you don't have insiders strongly pushing for it it won't happen.