The federal government had super strict emission laws for vehicles starting in the 70s. This was before computers were cheap and reliable enough to stick in average vehicles, so the way automotive engineers got it to work was to have vacuum lines to send signals to the carburetor and distributor. They probably could've done it with analog electronics, but you already have a free source of vacuum (the intake manifold), and there isn't an simple way to convert an analog voltage to a linear position, while you can do that with a diaphragm and vacuum.
Thanks for illustrating the nightmare that three decades later will still roust me from a sound sleep. Back in my pro wrench days, I had to remove-and-replace the head on one of those Hondas. What should have taken an afternoon soon turned into a hellish day-and-a-half of squeezing a vacuum tester.
For a good example, any American V8.