Pretty sure you can find schematics to make a BT100 printer somewhere ( https://en.wikipedia.org/wiki/BT100 ). You wouldn’t want to, but you can.

More seriously, I think the main problem is simply achieving a usable resolution for a 3D printer is way easier than for a 2D one. Hence why the real hard part (the print head) is using an HP cartridge instead of rolling out their own here. Given my quick googling, it’s usually that or building an inaccurate pen plotter and calling it a printer…

We’re not exactly great at economics too…

Because remaking the world to suit what robots we can make is more work.