But before you even got to the point of printing, the paper in a regular laser or inkjet printer wouldn't even feed properly if upside down!

I'm also willing to bet that whether or not the droplets are "fired" at the paper or not, the inkjet cartridges aren't going to work in an inverted position: they might not even supply ink in that configuration.

The only competition it would have would be a Microline ML184.

And when shuttle was developed, printers barely existed. Both inkjet and laser desktop printers were introduced commercially 1-3 years before the shuttles first flight in 1981, and weren’t very reliable yet. Desktop printers still aren’t as reliable as a teletype or dot matrix printer. There’s a reason airlines use dot matrix for printing flight manifests at the gate.

Ink plotters, teleprinters, and fax machines ruled the world. But plotters are dreadfully slow at writing text. Radio fax machines may have been viable if they were rugged enough. But they probably weighed as much as the teletype and were much slower - only real advantage is printing diagrams and photos.