The lack of vision at DSLR companies is mind boggling. Why can't I do light editing and post to Instagram directly from the camera? Why can't download the photos directly to a phone? Why can't I charge from a micro-USB/USB-C cable? I get it that pros don't need these features, but how hard are they to implement? The camera is already $1000+ dollars, how much more could adding a touch screen, a SIM card and a beefier…
I am not saying everything is perfect. But it seems you haven't done research on modern cameras.
Trying to put a whole phone stack in there isn't the core competency of any of those manufacturers (except barely Sony, though a different division). It's not just "slap a SIM and a beefier CPU" in there. Camera CPUs are highly specialised. So you'd have to essentially put another phone in there. That adds BOM cost plus reasearch and development of folks without core competency. Issues with software updates, compatibility, let alone battery life. All so you can edit a picture on a tiny 3" screen to post a 4megapixel version of a 24-45Megapixel original image directly to instagram?
Zeiss is coming out with a phone just with everything you've described. They're late. It will be huge. It will be incredibly expensive. Not sure I'd want to go that route.