Typically a lot of systems use electronics that needs programming but doesn’t need the intricacies of an entire PC plugged in, such as a Laser Pointer needing to connect to the PC to switch slides, and Traffic Lights needing to know their pattern switches etc.
In these cases we need a microcontroller or a printed chip specifically for these things that don’t need a lot of memory but have other features such as RAM GPIO etc onboard, which is where SoCs come in. This makes up 95% of the market share of big chip makers like ARM
