Why is it?
I can think of a few good Star Wars comics, but no great ones come to mind.
The original Marvel series was laughable, even at the time. Forget the campiness of an alien Don Quixote and a giant green rabbit. The entire series was pretty fucking awful. It was ridiculous how much the gang hopped around the galaxy during the period between ESB and ROTJ--like some shitty action show, they'd catch up to Boba Fett on one planet, and he'd get away again. And let's totally forget the ridiculous post-ROTJ stories. Ick.
However, I must say that one annual (#3) contained the closest thing to a great SW story. A standalone about two kids on a planet, one convinced to follow Vader, the other to join the Alliance. Great character development there, thanks to Mary Jo Duffy.
Dark Horse's run is insanely bad.
First, there's Dark Empire. It's not even most important that they didn't bother to make facts about Leia and Han's kids jive with the already-published Zahn Trilogy (forcing a silly retcon by the inexplicably employeed Kevin J Anderson a year later). Nor that they used Dengar, who was most certainly killed by Mara Jade in the Zahn Trilogy (forcing an even sillier retcon). Luke falls to the Dark Side, the Emperor and Boba Fett come back, the Emperor dies, the Emperor comes back, the Emperor dies again.... It got fucking ridiculous. It was like Star Wars by Rob Liefeld.
Crimson Empire? Overrated horseshit. Just a couple of Royal Guards beating the shit out of each other for about six miniseries.
SOTE was a decent book. But the comic sucked. It was essentially the "bonus material" cut from the book. And it didn't seem like that much of a bonus.
All the old-school shit like Tales of the Jedi? Dude, who the fuck wants to read about Jedi who are technologically advanced enough to have spaceships and hyperspace, but primitive enough to use fucking swords? Not to mention that, if you're using new characters, you have to make them at least slightly interesting.
The ongoing (the one that became Republic) had the best chance. Early issues made Ki-Adi-Mundi interesting. But just as it was getting good, BAM! Ki-Adi's out of the picture, and some douchebag Cherokee Jedi named Quinlan Vos is in. Oh, and he survives Order 66. Yay.
Tales had some fun stories. Unfortunately, they decided that anything printed therein didn't really happen simply because some of the stories were humor. There was plenty of shit to make up for the good stuff, though. Maul vs Vader? Fucktarded.
Infinities was so unspeakably bad it defies all categorization. What If meets Star Wars? Sounds like a good idea. But they were so incredibly fucking ridiculous. Leia becomes a Dark Jedi and Yoda crashes a Death Star into Coruscant? Silly enough for you? How about Vader becomes a good guy and re-creates his armor in white? That should probably do it.
Empire was chintzy as hell. First story, they decide that Biggs lied to Luke on Tatooine and they were planning this massive mutiny, which was almost stopped by Hobbie, who was planning another mutiny but wasn't ready to spring his. Also, immediately after AOTC, what do the heroes meet but a stranded Clonetrooper! Let's just totally forget that, by this point, Lucasfilm says all previous stories are canon, so there is literally nowhere to wedge stories like these, or Leia meeting an old boyfriend, or whatever other forgettable shit came out of this series.
Lt Janek Sunber was a brief bright spot in the series. An ethical Imperial Officer, often pitted against scummy superiors and forced into moral quandries. Two issues with him were as good as the aforementioned Marvel Annual. But then, well, the coincidence police decided that he was really "Tank," from Luke's throwaway line in ANH, and Vader found out about this and started using him as a pawn.
Dark Times? I've not even bothered checking it out. The time period is ripe for good stories, but they've proven again and again that's not their aim, so I'll save my money.
Finally, Legacy. This series is horseshit even by Star Wars comic standards. First, let's totally forget this little rule about Sith and the whole thing about Balance of the Force. The galaxy is ruled by evil Sith who wiped out the Jedi again! What kind of Sith? Fanboys like female Twi'leks, and they like Darth Maul, so how about a female Twi'lek Sith with Maul's tattoos? Every single thing in this comic is masturbating some fanboy somewhere, and there's so little attention paid to story, I had no clue what the fuck was going on after reading three issues, so I stopped wasting my money.
Sad to say, with fanboys enjoying Dark Horse blowing them with this series, and Hasbro also beginning to blow fanboys with comic figures you've never heard of, we'll see Darth Aayla Secura long before Yarna, Cliegg, Tey How, etc.
But, truthfully, why the fuck do all these comics suck so much ass? True, Lucas himself has gone to shit, but why can no one else tell a good story in this universe? Genndy Tartakovsky had no problem with it. The only thing I can figure is that Lucas won't allow anyone who's obviously more talented than him write a story set in one of his universes (as also proven by the Indy IV/Darabonte debacle). I guess he just didn't expect Clone Wars to be so good, and got rid of Genndy before making it an ongoing series. Who the fuck knows?
But I guess we'll have to settle for that, unless we get into stuff like Gilgamesh, which is historically significant but not especially good. Shit, even the oldest parts of the Bible aren't four thousand years old!