Another reason for the large CCD sensors in mobile/cell phones now, is that they are so much cheaper to make than just a few years ago.
What would make the biggest difference to a phone's image quality is a better lens in front of the sensor, but as phones are so thin, it's difficult to make lenses fit into that limited space.
The point of jpeg image processing was to reduce the memory needed to store images on camera cards, which were expensive to make, 10 or 15 years ago.
Today cards are so much cheaper to make and buy, that it's thought to be acceptable to have every photo taking up 6 or 7 MB each on the memory card (!!)
So we have phones with large image sensors, and poor lenses.
I suppose the idea is to do all the 'zooming' and editing in the image editor because the lenses are not yet up to the quality of even an average camera lens.
Why would they be, they are phones.