I have written a more detailed comment on it before, but 2d printing is much more technically complicated than 3D printing, and the resolution is literally an order of magnitude difference (0.2mm vs <42um) and the printer has to print full color on any surface with microdots in a very very short time. People would throw the printer out if it took 10 minutes for a single paper like a large first layer takes in 3D printing.
Open source Obsidian notes application.
The second brain part comes (I think) from the zettelkasten method of brain dumping all of your thoughts, notes on things you learn, etc… "On paper” in order to organize it and not lose it.
It is often recommended (along with to-do lists) for people with ADHD, and good for people like me with bad short-medium term memory.