The microcontrollers on these devices don't have MMUs. There is typically not even a USB interface. The microcontroller is in deep sleep mode saving power 99.9% of the time. During that time only essential peripherals are powered on and no code is executing.
A RasPi has no chance of running for 20 years off a single A-size non-rechargeable non-serviceable battery.
and just like any other IoT, using generic chips and stacks is cheaper.
run QNX or Linux on it and walk away.
there are DYI insulin pump monitors out there already that use Linux on RaspberryPi - see here: https://openaps.org/