When you opt-in, does it notify you of all the permissions the app will require?
- view network connections
- pair with Bluetooth devices
- full network access
- run at startup
- prevent device from sleeping
- view network connections
- pair with Bluetooth devices
- full network access
- run at startup
- prevent device from sleeping
Android 6.0 introduced requestable permissions, were critical permissions had to be requested (and could be denied) at runtime.
At the same time it removed all modals for non-critical permissions.
My cynical side believes that the reason for it not being as visible as other permissions is that platforms profit from the ad-driven app model, which itself heavily relies on an apps ability to access the internet.
That could also be why stock roms do not allow users to disable full network access on a per app basis. (...like, for example, the camera permission.)
For example, just trick a user into clicking a hyperlink to another app like a browser which does have full internet access, and you have successfully exfiltrated any data in the URL.
I mean sure, you could do that, but it would be complicated, conspicuous, tiring for the user and you would still only get one-sided occasional transfer. It could exfiltrate data, albeit suspiciously, but it wouldn't work for ads .. which are the likely motivating factor.
Other motivating factor may be tracking, which google and vendors want to do, but I'm not sure what the stance would be on others tracking their users.