Ink delivery is likely the main challenge (although I've seen some low-res attempts), combined with the speed and precision needed for a good printer - reaching a few hundred DPI requires positioning things quite precisely. Laser printers are interesting, but then you need specialized parts like the drum that I'd expect to be difficult to produce in single quantities.
Open pen plotters are a thing, but again not typically used for normal printing duties.
You'd never run out of toner at least.
Edit, answered at least one question: yes engravers do 500 dpi routinely. Here's one: https://www.troteclaser.com/en-us/knowledge/tips-for-laser-u...
Also, high power lasers are consumables.