Even something that seems as simple as "sous vide" cooking, which is basically a heater hooked to a thermocouple, took a lot of little innovations to make practical to hand to the masses.
And then, there's the general improvement in motors speed, precision, and cost, along with any number of advancements here and there and everywhere to make it practical.
Could someone thrust back to the 1970s and given a fairly substantial budget make some kind of 3D printer? Probably. But it's slow, extremely expensive, and can print various sizes of plastic bricks and spheres and other very algorithmically simple objects, and in rather low quality without many, many years further development. I can think of many ways of bodging on various improvements, but they're all going to have their own compromises, not be garden paths to what we now think of as modern 3D printing. (For example, someone could bodge together a machine that offsets a rod on the printer head, and then in the offset space, has an object to be "copied", by basically banging into the object with a very crude sensor, so there's no generation of geometry at all. But this is going to be clumsy, inaccurate, and full of very complex and disheartening limitations.) You're not going to be printing Dwayne "The Rock" Johnson's face embedded into a toilet [1] or anything, at 1MB of geometry. It will be commercially useless and inaccessible to hobbyists.