Network is a permission on Android, it's just that phone manufacturers and likely Google don't want you to be able to control it. Most custom ROMs, including GrapheneOS expose it properly, often at the install dialog.
Some time ago, I used a module for Xposed on Android called XPrivacy which did exactly that. Yes, creepy app, you can have my location. It's Antarctica.
It does look like Xposed has successors, but my current approach is to just be selective about installing apps.
I use netguard and forbid network access by default for all apps. Mildly annoying for apps that need network access as I have to approve, but it's worth it.
The vast majority of apps need to use the network, at least sometimes. Eg turning network on to download podcasts then off to listen to them is annoying.
Depends on what apps you are installing. I love denying access to the network for games. It removes almost all ads from them. Even beyond full deny access, NetGuard gives you a lot around the conditions in which an app can access the network. I'd prefer if I didn't have to do any of this and the OS was on my side though.
On an unrooted Android you could use App Ops to do some of that with Shizuku.
I assume they don't expose it to users because once most people start to do that apps would start to implement detections, like if it spoof your location to a certain area then that area will get you "permission denied" error anyway, or I believe some apps do check that if your contact book is empty it assume you didn't give the permissions. It'd become a lot of work to implement a convincing spoof for most permissions to be blocked.
On play store you can see the permissions that an app uses and they are grouped by category. Have full network access is set in the "others" category, same as notifications and vibration. This is a category where (supposedly) permissions are automatically granted.
But to be honest, other similar dangerous permissions like "view network connections" and "receive data from internet" are also there, categories are for "camera", "microphone" etc.
I suppose that the average user is more concerned about specific features, and since basically almost all apps require internet it may be there to avoid noise.
Still, an "internet" category would have been nice...
The reason why internet access/downloading from the internet isn't a "major" permission is that asking about it would let people conveniently disable it for any offline apps with ads in them to remove the ads. Google doesn't like that, obviously. Of course, you can still disable your wifi/mobile data connection entirely, but it has friction that most average consumers won't trouble themselves with. But if the app asked if you wanted to give it internet access on launch, Google's ad revenue would probably be visibly affected.
