Ah, gotcha.
Problem is, designing for interchangable batteries at all adds to the size and weight of the object… connections must be made, the battery must be made robust enough to withstand handling, you have to worry about the battery shorting out (at current energy densities, that isn’t a laughing matter – websearch will find videos showing high-density batteries igniting or exploding), and generally it isn’t compatible with the ultra-compact implementations we’re demanding of phones. Cameras allow more space for batteries, AND generally aren’t drawing as much power, so they have more flexibility in this regard.
It’s engineering… The bad features of a design are usually not malicious, but are the result of trading away one thing to achieve another. If you’re willing to go back to phones being the size of a small camera, sure, we can do it. My Palm Treo has batteries I can swap out., but it’s rather chunky by current standards.
