You're assuming it's their choice. It's much more likely that they don't own all the IP and can't get the relevant rightsholder(s) to agree to make things public. Notice that they say "we were able to share" and mention "work[ing] through constraints" when talking about sharing more detailed schematics.

I imagine they can't say this explicitly because the terms of their business relationships are themselves confidential and they don't want to say anything that could jeopardize those relationships.