st and nxp and atmel make cortex-m4 and cortex-m7 microcontroller
price >6$
and at this price i can buy cortex-a8 1ghz + sdram chips
why they manufacturing cortex-m4 and cortex-m7 at this price and i can buy high performance cortex-a8 1ghz cpu at same price ?
Why would someone make cats if there are cheaper dogs?
Other than that, µC and µP are different type of beasts, for different purposes, price and computational power aren't the only two factors, as mentioned power consumption, connectivity, ease of use, are other factors to consider. You may find and M3 or M4 under the seat of your car just to adjust the position, it has the required peripherals in the chip, probably could be done with an M0 but for some reason they found M4 a better option, for example already used 40 times in the same car but the M0 won't cut most of those applications.
JS