This supposes that you have seen all 6 films and have not read much more into the fan fiction (there are hundreds of books, especially the new jedi order ones). Maybe you played some Star Wars battlefront or maybe Dark Forces – hell maybe even Force Unleashed. All in all, you know that Jedi suck.
In the first two films, you had a whinny wimp of a jedi but still pretty cool in what could be done. In the third you had him against a Sith Lord and Empreror who shoot lightning out of their hands and can’t be beaten (except by each other). Sith are awesome but they have power issues. The 3 prequels showed you how stupid the jedi order is and why it essentially deserved to be wiped out. Not a single person who watched those movies found an ounce of guilt to watch them all die (well maybe the kiddie jedis). Other than Anakin, Obi-Wan and Yoda, you had dozens and dozens of jedi who just sat down for 3 movies while the Sith is jumping from planet to planet, throwing stuff, beating people up – basically doing what they want to do. Oh, and more lightning. When Anakin dies in the final prequel, he’s still a jedi and boy are we happy to see him die.
The games are interesting in themselves. Dark Forces you were a jedi of sorts but not any jedi I’ve ever seen in a movie. You blew crap up all the time and had great powers. Knights of the Old Republic let you play good or evil and I’ll be damned if anyone went full healing rather than full lightning. Force Unleashed is you as a bad guy, plain and simple. If at the end of the first one they said “now you’re good, gimme your lightning” I would have thrown up.
The Star Wars franchise was built around the samurai code of honor – mortals versus demons. Then George humanized these demons and took away all the honor from the mortals.
So here we look at The Old Republic and class choice. There are 4 in the Jedi order and 4 in the Sith Empire but they pretty much are mirrors of each other. So if you have a choice between playing a goody two-shoes jedi who runs around healing and throwing rocks at people and a sith who shoots lightning and burns people, where you going to go? The same place over 75% of the player population is going to go.