because for a lot of things you don't need that much cpu power. Creating something that can read several sensors (switches and buttons are also sensors), and p

because for a lot of things you don't need that much cpu power. Creating something that can read several sensors (switches and buttons are also sensors), and putting aggregate status updates on a serial line, or displaying status lights, triggering relay or something similar can be done, on decades old gaming consoles, and is probably one of the most common use of processors in the world today. In fact it is easier than trying to use modern cpu, that wasn't designed for that. Not everything is about computation, in fact in terms of units sold its probably a minority.