You know about computers, right? When they make Integrated Circuits, why do they wrap them in plastic/ceramic/other and connect them to everything else with pins and stuff? Seems inefficient to me. Why can't they just print them in silicon directly onto the surface of the Printed Circuit Board? I suppose giving them a case provides them with some protection, but couldn't they do that another way for the whole board instead, like by, I don't know, laminating it very thickly?
Computers? What's that?
Packages with pins allow for safe storage and manual montage of the ICs, as well as for a relatively easy way to replace them in devices. The packaging might have built-in solutions to cool the structure. But sometimes the chips are mounted the way you describe.
You sometimes might see one or more black blob-like objects on some devices' PCBs. These are bare silicon dies, connected to the PCB traces using thin wires, and then sealed using black compound. The downside of this method is basically lack of a way to repair if the IC gets faulty, applying sufficient cooling might be harder too. Storing bare silicon dies is also problematic.
OP asking if Systems on a chip have been a thing or not circa 1992 textualized.