It doesn't say anything about the actual demand, but about human tendency to take the path of least resistance. There are many things that might benefit me but I won't go out of my way to do, and that's the same for everyone else as well. Opt out means that I don't have to do anything but do get the benefits of that thing.

What is perhaps problematic is that it's not visible enough that this feature has tradeoffs or that there is an option to opt out, or even that the feature exists, but that problem exists for all sorts of software on the phone.

No it doesn't. It says something about network effects and the psychology of opt-in vs opt-out.

Not the psychology so much as the behaviour. As in, I can get away with doing X by making avoiding it opt-out. The psychology, aside the decision to make an effort, I imagine as being aware and informed in terms of that decision. Which falls back to the behaviours performed to prevent that.