I'm not sure you are right here. The sensor size (and the lens speed) has been one of the key things Apple marketing has been leaning towards in the last few generations. Tech reviewers tend to repeat it back to their audience, which eventually lead to general consensus of Apple's camera system being superior.
Sensor size in smartphones is also "highly manipulable", because the smartphones are very flat and have serious angle of incidence issues as the lens is too close to the sensor. If consumers demand larger sensors, sure it can be done - but it will reduce the amount of light that reaches the edges of the sensor, eating the possible increase in image quality. Smartphone cameras are limited by thickness, not by sensor sizes.
