Why are you comparing two completely different things?

MCUs and CPUs are not comparable, even they seem similar.

MCUs are created to control devices on lowest possible level (like hardware support for USB, I2C, SPI), maybe with some basic DSP stuff (like digital signal filtering). Their strong point is not calculating, except if a MCU has instructions for more complex arithmetic.

CPUs hovewer are created to compute stuff. All kinds of stuff. To control devices CPU has to its disposal external I/O controllers which are held chipset.

CPU cannot do anything by itself, you need crapload of other chips in order to do something.

MCU on the other side is autonomic, for instance if we take AVR microcontroller like in Arduino, to make it work we need one resitor on RESET pin, two caps on VCC and GND and if you want to program the MCU - a hardware programmer.