That’s because most of the properties in the testbox object (as well as many of the properties in box.json in general) aren’t actually in use yet. When we created the default box.json we had a big dream-fest of all the cool stuff we could probably do with it, but much remains to still be implemented. ForgeBox 2.0, when complete, will do a lot with the box.json for packages to pull metadata about the package.
I think the only command in the testbox namespace that actually uses the box.json data is “testbox run”. You can thumb through there to see what’s actually in use. Anything you think we should be using, please put in a ticket where we can discuss and if we all agree, then we would love to have your help with some pull requests to make it a reality.