Good image quality can indeed be achieved under 500KBs, but the problem is every phone camera does not have good autofocus. especially people using lower MPs camera which
produce smaller image size mostly have fixed focus cheaper lens. And if they are not camera fanatics, they will not understand the focus plane of a fixed focus lens. a Higher MP camera
even if uses fixed focus lens, can cover up a not so well focused image with higher resolution , thus higher size. I am not talking for people who have good camera phones. There are still people
with fixed focus lens camera phones.
Thanks & Regards..
"If you want to do something in a better way, do it yourself !" --Nepoleon Bonaparte