What happens in that case is that competitors copy your hardware and throw the open source firmware on it to undercut you. Consumers don't know how to differentiate your products without marketing/segmentation and OEMs mostly care about the BOM cost. It doesn't matter much that your competitors are 2-6 months behind because they're still killing the long tail sales that sustain a company.
Note that I'm still pro-open source, but I've seen this cycle play out in the real world enough times to understand why manufacturers are paranoid about releasing anything that might help a competitor, even if it benefits their customers.
> What happens in that case is that competitors copy your hardware and throw the open source firmware on it to undercut you.
The entire premise of firmware is that it's specific to the hardware. By the time they "copy your hardware" it's already obsolete. Also, that's the thing you're actually selling. Your firmware sucks. Nobody wants your firmware unless they have your hardware. People are paying you for the hardware, which is the thing cheap competitors can't make as well as you or you're already screwed.
Note that I'm still pro-open source, but I've seen this cycle play out in the real world enough times to understand why manufacturers are paranoid about releasing anything that might help a competitor, even if it benefits their customers.