How often do Jedi Knights use the Jedi Mind Trick? And isn't it far, far more often than how much the Sith Lords use it?
The Star Wars wiki says that the Jedi do their best to limit its use to ways that serve the greater good (e.g. Obi-Wan's moment with the drug dealer in Attack of the Clones), and that the Sith have no such qualms, but when are we shown that? Qui-Gon Jinn sets up the chance to get young Anakin out of poverty, Obi-Wan Kenobi gets Luke and the droids past the troops, and things are made smoother for our heroes. Since the Dark Side of the Force is "quicker, easier, more seductive," wouldn't the Sith be even more inclined towards using it? THEY COULD HAVE. It's kind of like when Peter David got to write a comic book starring Popeye, got thinking about how in the cartoons Popeye could only properly fight Bluto if he ate spinach, and thought Why the hell did BLUTO never eat the spinach?! He ate that, he would've been strong enough to punch Popeye into next Tuesday. But even when they're still surrounded by a Sith-unfriendly Republic instead of a Sith-friendly (or at least -friendlier) Empire, the Sith aren't shown using it.
Instead, what Chancellor/ future Emperor Palpatine did with Anakin in the prequels is, I'll be profane and blunt, straight-up mind-fucking. Psychological twisting, well-practiced by manipulators and abusers, to get someone to do what you want. No Force needed, even though this way it takes years for him to bend Anakin to his will. Of course for about two-and-a-half movies, Palpatine pretends in front of Anakin that he has no Force powers, but c'mon: he's still the far more practiced practitioner of it. (Remember what he was able to do to Darth Plagueis!) If he'd needed to use the Force without a Jedi picking up on his use of it, he would've done it. He could've convinced Anakin that any hand-wave thing was a nervous tic. Pressures of running a galaxy-spanning republic that threatens to unravel; he'd understand. (Palpatine can't unwind by getting laid, either, not that he seems interested in sex, but that's a digression.)
Events move quickly and disastrously once Surprise Sith is revealed to Anakin -- the last half of Revenge of the Sith, which ends with Anakin christened Darth Vader, almost all Jedi Knights slaughtered, the Republic gone, a particular death on a medical bed, a particular near-death next to a lava flow, major medical intervention to be sure Vader survives: there's no time for Jedi Mind Tricks then. But then there's that, what, 20-year or so stretch between Revenge of the Sith and A New Hope: Vader and Palpatine probably used the Mind Trick sometimes then, right? To pass the time? Who's going to stop the scary walking-scab guy and the towering Force-choking guy from playing pranks?
(Oh, God, the image of Vader and Palpatine as Beavis and Butt-Head has just popped into my brain. I've already seen Vader and Boba Fett as pimps, so is Vader and Palpatine on a couch such a leap? Huh huh, huh huh, you said "Kit Fisto"...)
Obi-Wan tells Luke that "the Force can have a strong effect on the weak-minded," and Kenobi certainly seems capable of spotting who is weak-minded, but that can't be everyone Kenobi encounters or there'd be no challenge. Star Wars does not have an Idiot Plot, which (as James Blish codified it) can only work if the characters involved are idiots, but it can be a liiiiittle convenient. (And only now do I realize how much of a risk George Lucas was taking by having a key detail in his story be literally a Hand-Wave Moment (hey! It has a TV Tropes page!). Why hadn't I noticed that before?)
Meanwhile, the Sith are surrounded by the weak-minded. Toadying Imperial officers, the perhaps mentally decaying former clones who are now stormtroopers (seriously, unless the Kaminoans are still pumping them out, whatever clones are left by the time of the original trilogy are decades old; how are they holding up?), Death Star employees traumatized and cowed by all the miles-deep shafts they have to work next to without benefit of railings (Vader and the Geonosians could've taught Leonidas the power of shafts, but again, digress I do); it's a freakin' dandelion field of people they could mess with. But other than the shaft thing, there's nothing passive-aggressive going on. You piss off Vader, he stands right in front of you and Force-chokes you. Hands-on. So to speak.
This is making me want Jedi pranks. Probably means I would be a bad Jedi.
Feel free to correct me and to explain things. Because, seriously, why not more Mind Tricks?