There are so many people building their own 3d printers that there are kits for it, guides for it, and countless swappable versions of any kind of part you can think of, and hundreds of companies ready to sell them to you.

But there is seemingly good motive to want your own 2d printer. One is that manufactured 2d printers print secret codes on everything you print in yellow ink making your printer useless for gorilla activism. Another is the lost sense of control that comes with that. Some more broadly valid reasons is ink cost and lock in. Also shitty software that lives on your computer to use it with a history of installing spyware, and agreeing to licensing.

What should be a valid enough reason on its own is technical interest. That's the main reason people build 3d printers.

There is a large counter culture around 3d printers obsessed with their ability to have any item without having to accept the constraints of or pay a 3rd party. It gives a kind of sovereignty over 3d space and the objects in your world. But if that's something a large number of people care about shouldn't we pause for a second and consider we don't have that in 2d space. Sure you can draw but you have always been able to sculpt. And you can draw without hidden markings, and 3rd party software, and licensing, and vendor lock in, as well you can sculpt, as well you can 3d print, but you can't 2d print.