Why is this? Let's see if we can find out...
The first attempt at telling the X-Men story on screen was a short-lived venture called "Pryde of the X-Men" that never got beyond a pilot. It was quickly shelved, and what's interesting to note is that three of the main characters (Kitty Pryde, Dazzler and Colossus) never showed up in the subsequent X-Men animated show, and another (Nightcrawler) only got limited appearances. An attempt on Marvel's part to clearly set apart this team from the last one?
Whatever the reasoning, it must have worked because "X-Men" became an extremely successful television show, running for 5 years and remaining the longest running X-Men show (and one of the longest running Marvel Animated shows) to date. It featured a classic line-up and was extremely faithful to the traditional story-arcs of the original comics. To this day many X-Men fans credit their interest in the team to this show.
The only other X-Men appearance in the 90's was the generally disliked "Generation X" made-for-tv movie which did so poorly that most fans don't even mention it except to ridicule.
In 2000, Marvel decided to take the X-Men out for a spin again, this time moving away from tradition and instead imagining the main team as teenagers who attend public high school. This allowed for a more character driven, kid-friendly show that better fit the expectations of Saturday-morning audiences. It also was a surprisingly good show. Though the dialog was weak at points, the characterization and plotting was quite strong. The main strength of the show was treating the characters as teens struggling both with normal teen issues as well as the pressures of their superpowers. This made for an extremely accessible show, not only for comic-fans but also for the average viewer. In fact, it was this show that got me into comic books in the first place, and I've gotten several friends hooked on the X-Men through this show as well.
The show lasted into a 4th season, and left a lasting legacy in the Marvel canon as an original show character (Wolverine teenage girl clone, X-23) went on to become a regular member of the comic team and even a main player for a time on X-Force.
Also in 2000 was the debut of the live action film "X-Men." This featured the most well-known characters in lead roles, but contained a completely new storyline and dramatically changed character ages and in some cases, entire personalities. It did well commercially, but reviews among fans were mixed. The sequel, "X-2" was loosely based on the comic story "God Loves, Man Kills" but again changed character relations and personalities. The third in the trilogy, "X-Men: The Last Stand" tried to retell the Dark Phoenix arc, but turned into what is generally seen as a muddle of cameos and poorly executed and confusing storylines.
In 2009, Fox decided to try again with the X-Men films (which had been good moneymakers despite poor reactions to the third), and featured the most popular X-Man character, Wolverine in an origins story.
"Wolverine" proved to be a fun romp, but once again strayed too far from comic cannon to satisfy fans -- instead antagonizing and alienating many of them.
However, while the big screen was failing, the small screen scored a success with "Wolverine and the X-Men" which featured a solid line-up of favorite and currently featured characters, and a solid storyline that, while new, paid respectful homage to cannon. It's premature cancellation after only one season was mourned by many fans (especially this one!).
2011. What's next for X-Men? We've got another film coming up. Which, if you've read any of my previous posts on the subject, you'll know is being viewed with trepidation by most fans. And no wonder, with the track record Fox has made itself on the films.
At the same time, Japan is due to release an anime show, featuring a line-up of traditionally popular characters. Since X-Men animation and Japan's anime tradition are both strong and well-respected, there's interest and hope for something good here.
So looking over this colorful and relatively extensive history... what trends can we notice here?
Canon works. It's canon for a reason, and the comics have had 40 years to figure out how these characters work.
It's a sad but true fact that the time constraints of a film simply cannot do justice to the varied cast and adventures of the X-Men. There are just too many characters, and anything less than a full-length season is just going to delegate most of them to cameo roles.
And financially, a full live-action season would still run far, far less than making a big budget film.
So why haven't we seen a live action X-Men show yet? Two reasons. First of all, up until recently, doing that kind of special effect-work on TV was simply not financially feasible. However science fiction shows are showing up more and more on prime-time television -- to say nothing of cable. So that objection is pretty much out the window.
Second reason? Back in the late 90's, the executives saw two options. To make a film, or a live action show. They chose to go film. Their reasoning was that they couldn't promote both at the same time. Which is a very valid reason. It's just sad because I feel quite strongly that, in the long run, a show would have proved a far more satisfying experience than a film.
I could be wrong. They could have hired a horrid writer, cast terrible actors, decided on a corny plot...
Or it could have been wonderful. They could have decided to follow the comics, telling the story of the move from New York to San Francisco... or even better, they could adapt Joss Whedon's run on "Astonishing X-Men" which still remains (IMHO) one of the finest bits of X-Men story ever.