Undoubtedly, 8-bit processors are much simpler to integrate into a device. As it depends on the hardware requirements that are much relaxed. Everything is affordable, additional circuitry, power supply and the interfaces.
They can be as small as the SOT-23 package. Due to the greater insulation distances, low leakage currents distances translate into low idle power consumption. Devices such as pico/nano power AVR and PIC devices that can run on a coin cell battery. On-chip EEPROM, on higher density devices it's very unique to implement as almost none of the 32-bit devices has real EEPROM.