3D printers don't have anywhere near the resolution of 2D printers. Take something like a $300 Epson photo printer [1]. It has 5760 x 1440 dpi with 6 colours!
A Creality Ender 3 Pro, a common budget 3D printer, has an accuracy of 0.1mm. That's an equivalent of about 254 DPI.
Of course, that's just the positioning. If you're 2D printing on a 3D printer by mounting a pen to the end, you're also limited by the thickness of the pen tip.
In any case, you could certainly draw text, but you'd only want to use a font that relies on thin lines, nothing thick. Filled in spaces would be difficult, and of course, photos are just completely out of the question.
As mentioned in a sibling comment, really you'd have just reinvented plotters which have existed for decades.
Yes but it is expensive and slow, rarely big enough for A4 (or Letter) and would be plastic. Additionally it would be maybe up to 4 colours. Not as in CYMK but as in 4 colours total no mixing.
Unless you do a lithographic print but they need a light source to be seen.
Also you can print pixels. You convert to G code so it is made up of lines.
