It stems from my own personal likes and dislikes and from some gaming situations I've been in. First of all, I've never been fond of Magic Users (and come on, that's essentially what Jedi are). A great deal of this had to do with the increased complexity of running them—at least in combat situations (whether this complexity was real or imagined is up for debate). Simply put, it was a lot easier and more 'rewarding' for me to have to deal with folks swinging swords or shooting arrows than it was to have to pause and look up spell effects—which were often a bit vague as to their exact functioning.
As a player in several games that had magic-users, I was also frustrated by how long it took for them to actually DO something. In Shadowrun and Mythus, for example, we always had to pause for someone to look up something then try to decipher just what would do what. Yes, part of that is the GM's 'fault' for not knowing the system (though honestly, who CAN remember all the myriad of details from system to system). But it did seem to be a 'truth' in most of the games I played.
The Star Was D6 Force system was no less 'vague' in a lot of areas. Taken literally, for instance, it would be possible for a Force user to use telekinesis to move items that were on another planet or even another star system (if you took the Proximity modifiers at face value). I have spoken about the inconsistencies of WEG rules before—and the force system is one of those areas where this is showcased. Some powers would be affected by proximity, others would not, seemingly without any rhyme or reason. And unfortunately, this did cause several instances in my own game where I had to halt the proceedings to think things through. And once again, everyone else was waiting for the 'magic user' to do his thing.
Still, it was never /too/ bad. We got to know the various Force powers and what they could do. We came up with house rules to iron out the wrinkles (a time-honored gaming tradition). But things got complex again as gaming supplements began to introduce new powers—some of which could be VERY unbalancing to a campaign if used as-written.
So for my own sanity, I've been compiling a master list of Force powers. I've been weeding out the ones that don't work and trying to solidify the ones that do. And honestly, I'm trying to keep Force powers 'limited' to what we see in the movies (and perhaps some variations on that). I do not like the trend towards more and more fantastical powers that I've seen in some of the novels (i.e. Luke constructing a castle for himself using his mind). The Jedi may be a magic user, but he isn't a freaking wizard and I don't want him to become one.
Some day, I'll post this revised powers list—but I still have one major hurdle to overcome: Telekinesis. This is the most vaguely defined yet often used Force power of them all. If used 'as-written' it could be a game-breaking power. Afterall, why use a lightsaber when you can hit someone with 10 metric tons of telekinetic force? Why not just pluck the weapons out of the hands of all your enemies? As written, it wouldn't be difficult for a powerful jedi to do. And yet that isn't what we see in the movies—and for me that is a major guideline for play. In 'limiting' the powers to that, I have taken some flak in the past (from online gamers, that is), but I still feel it is necessary. After all, I want to play STAR WARS not ALL POWERFUL WIZARDS WITH LASER SWORDS!