I’m not sticking up for car manufacturers, but at what size or capacity should you be required to document and publish these things? It requires employer time and effort and has a cost associated with it.

You're talking about things that by definition have to be documented and internally published in order to design and build the powertrain in the first place. You can't design a computer-controlled automatic transmission without documenting the shift points.

The cost is therefore essentially nothing, because the information already exists. Just copy paste it into a PDF and put it on your website.