I think mostly because they don't need to have that much processing power compare to a smartphone, due to their bigger lens/sensor - so they don't need to use h

I think mostly because they don't need to have that much processing power compare to a smartphone, due to their bigger lens/sensor - so they don't need to use higher end processing unit. You can delay the postprocessing to a dedicated (external) software so to say. One big advantage you have with dedicated hardware also is the reduced need to have a virtual interface (though UX is quite often in dire need to be improved on them, especially for advance configuration). A bit like knob are better in a car in a general way. But to be honest, at the end, it's clearly a difference of philosophy. I'd wager that the smartphone maker have better understood the market than the camera maker for a while.