There is nothing complicated in the construction of a cheap 3d printer. Electronics is simple as well. We could already make them easily in the late 80s. Why?
You're young, aren't you?
It's been covered above, but here's my 2 cents' worth:
Looking at someone having their own personal setup.......
Speed: If you just look at the trend expressed by Moore's Law, in 1980, you were getting around 50,000 transistors on a chip. Today it's around 50,000,000,000. That's a factor of 1,000,000. Assuming this translates into an equivalent effect in processing speed, something that would take you 1 second today would take more than 11 days back then. A single "oops" you would think nothing of today and undo in another second could set you back weeks. Manual scrutiny of code and actions was much more necessary in those days.
(For reference - the IBM 370
mainframe I was working on in 1980 had 256
KB of core memory, with an OS on one 70
MB hard drive and the company files on another, with a third as a sort work area. This was a company with branches all around Australia.)
Cost: All this is assuming you had the supporting resources such as memory (which was measured in KB) and storage (a 5MB HDD cost thousands of
1980 dollar$)
Awareness: Back in those days, you did not have the instant communication channels you have today. It was magazines and who you knew - and those circles were usually very geographically limited. You could have someone 20 miles away who had a great idea, but you would never hear of it unless it made publication somewhere - and you got to see that. Today, someone could have an idea (good, bad or indifferent) and the whole world could know about it within minutes. In 1980, 3D printing as a concept would not have had the exposure, so there would not have been the interest and, thus, development by interested hobbyists - and even if there was, it would more likely be by individuals working in isolation or, at best, in a very small group. This sort of tech in schools was unheard of.
These factors were less of an issue for industrial and commercial organisations because of their very nature.
To put it another way ... Could a single human being build one of the pyramids? Given the knowledge of how, the physical stamina and living longer than Methuselah - yes. So grab your chisel and get started.... You can do it!!