This question comes up a lot. 2D printers are actually significantly more complex thans 3D printers. The rrason 3D printers game much later was a materials problem and the fact that there was already injection molding which gives much better results for production, which means it took a while for big players to see the value in it. Here is my further comment on another post:

"Tons of 2d printer challenges.

The ink jet head at a resolution of <50um (as opposed to 3d printing resolution of usually >200um)

Combined with printing on many different surfaces and such: cardstock, printing paper, glossy, weights, stickers, etc...

This project "cheated" (I mean that not in a negative way, tons of open source hardware projects use proprietary components, my own does too for now) by using a proprietary ready-mades printhead, which saves the most cost and effort of the whole machine, and is the component that causes the most issues, generally.

I definitely want to try this out too."

https://feddit.nl/comment/20418339

Is there a real need to have paper over plastic at this point? So many things now require a plastic piece. Not seeing where paper is still being used to retain records or utilized for gaskets… I suppose cardboard but even then not much has changed in that tech.

3D Printers that are turned into Pen Plotters is also a neat project.