Totally bizarre marketing on this one. The director was blathering before the movie hit theaters that there was already an extended and ultimate cut coming out within 6 months of theatrical release. Then everyone was mystified it was a theater flop. Well, gee.
If you know about the mythos, then you know why this happened. The movie was talked about to be a two-parter, then how they were going to mix it down to a single epic film, while keeping all the fans and non-fans happy. The movie could have easily spanned multiple films, but the way they did it was very respectable to the original source material, imho. (IMHO.) The "extended cut" was much better than the original film version (see; "director's cut", it's not that unheard of) and the "ultimate cut" has another complete movie interspersed with the original film, so that fans of the source would get what they wanted from the movie.
It wasn't necessarily a theatre flop, although it reportedly grossed $107M+ with an estimated budget of $120M-$130M, however, the bank is in when it comes to marketing after the fact. DVD and merchandise sales and such are certain to continue for years.