It feels like the camera was the obvious add-on to the smartphone on the timeline we live (arguably the only one?). However, consider the point in time where they had a working phone (calls and communication) and were deciding on what to add. Someone should have pitched the camera. Imagine another person pitching the addition of health sensors to the device.
Addition of the camera to the smartphone funnelled in a lot of money into computational photography research. Within 2+ decades, we have astonishing development in camera technology (partly) because of this. On the flip side, our civilization has turned into a picture-first civilization, where pictures are a central part of every moment in life. One could argue that we live as performance for pictures on some level. Social media adds to this, and we have a whole lot of emotional issues that come with the social media stuff.
Consider the alternate reality. The person pitching the health sensors won. Within 2+ decades, we have amazing health sensors on every device. People are healthy, has longer life expectancy. We give way less consideration to how picture perfect life's moments are. Social media is not messing our social fabric as much as it is doing today.
This would be an interesting scenario to explore on a science fiction. Someone should write this, and let me read it!