...because the game does not grovelling revolve around Luke, Han, Leia, or unlikely cameo appearances by minor characters, or any of that shit. It's protagonist is not a Jedi, has no special powers beyond their blaster rifle. Today Disney/Hollywood execs, on top of their many other sins, are convinced that you need 'familiar faces' in games. The Star Wars galaxy is massive and the likelihood of running into movie characters is negligible, meaning implausible cameos shrink the breadth of the setting. This constant fixation on what someone like Han was doing between movies is really constricting. Dark Forces instead created a new hero. It created a feeling of isolation and self-reliance, with a brand new character, Kyle Katarn.
You are just one mercenary among thousands of worlds, operating against the Empire without any Jedi powers, on distant isolated outposts, as the majority of action in Star Wars must be. Battles must take place daily, between pirates, rebels, outlaws and imperial special forces. The sequel is also amazing, and is something that would never happen now; an original galactic-level threat like Jerec, being handled without reference to the movies, by someone on an independent hero's journey to Luke. Kyle Katarn is the subject of memes; the Chuck Norris of Star Wars. Ten years after buying out Lucasfilm, there is no word on whether Kyle Katarn even exists in modern canon. It would be so easy to remake Dark Forces in Unreal Engine and release as a ÂŁ9.99 game on Steam, GOG, PSN, etc, re-canonizing the plot by altering a couple of lines of text.