Why?
It wasn't very good.
Don't get me wrong, it's not like I don't like the show (own the series and "Serenity"), but, in truth, it just wasn't anywhere near as creative as so many of the fans would like to think it is. I know in truth that it was cut because of the producers pulling a switch on us, but I can't attribute the series' lack of commercial success on anything other than no demographic picking up on Joss Whedon's apparent need to keep a faux-witty series on the air, regardless of how utterly unoriginal it was (How long did "Buffy" and its spin-off run?).
Sure, I'm about to get flamed by the ridiculous amount of brown-coats I'm sure there are here, but, face it, it wasn't a very intellegent show. It wasn't a very well-written show. And it CERTAINLY wasn't a very original show.
I really, REALLY wish people would stop whining about it.