Most PID applications are not IoT. Many use a cortex M0 which doesn't have hardware float support, or non Arm, even 8bit. When you are selling millions it pays to use the cheapest part you can get away with.
What do those things go in anymore? Surely there are asic pid controllers that are insanely cheap? Tuning an analog one I can see probably doesn't make sense anymore, but there is something nice about being able to do that with a screwdriver instead of jtag. What do these M0s go into?
I used an 8-bit PIC micro a couple years ago for power applications (think non-IoT lighting). The specific microcontroller we used had nice peripherals for sensing, and controlling diodes, but no FPU. I remember looking into getting something external to handle the PID, but the cost and board layout constraints made it challenging.
