Det_Bullock: Therey were still incredibly common, as ubiquitous as gamepads today if not more, even the arse end of nowhere (like where I live) if there was a computer shop it kept at least a joystick or two in stock.
SimonAmor: Regardless of what you claim, certainly when this game came out, not everyone had a joystick.
The world was (and is) not only first world nations. In fact, most people lived in Third World nations (and the same is true today). And most people couldn't afford a computer, and even of those who could, not everyone had money to spare for additional things, like joysticks.
Joysticks weren't the costly things regarding PCs at the time, there were plenty of cheap ones (they weren't a niche luxury item like today and flight simulators were very popular, for every CH or Thrustmatser there were 100 Quickshot), the expensive stuff were soundblaster cards (I only ever had a cheap "compatible" that wasn't compatible at all), RAM memory banks and other costly hardware expansions that I could never afford.
Hell, my DOS PC was very cheap by necessity and crashed with anything that was more CPU-intensive than Wolfenstein 3D or some old Apogee sidescrollers, I had to skip all the cutscenes to be able to get to the end of any mission in X-wing and many couldn't be completed anyway because it crashed after 15 minutes by clockwork (and of course had no sound).