Yes, but then it would be slightly heavier and have way too good of a battery life, reducing power bank sales and having the phone last longer without needing to be replaced due to battery degradation.
My plastic cover doesn't provide power, no. My cover levels the back to be on even level with the camera — much in the same way the proposed larger battery would.
Because it adds more bulk to an already massive device, and it'd be nice to have the device itself be able to withstand bumps and scrapes without needing extra padding.
I mean, if you want to withstand bumps and scrapes you need padding. But without a case you need the padding to be glued to the phone directly. The bulk remains the same no?
Give it a few more years. At this rate, by 2028, the entire back of the phone will be camera bump and you'll be able to lay it down on a flat surface at last.