Because of enverything you'd have to put in it...it would be this like epically long movie.
You could make it shorter, but to do that, you'd have to cut stuff out that would make the movie weird and kinda choppy and it wouldn't flow and you'd leave people wondering what's missing.
Something that spans thousands of years would either have to be a series of movies, in which case, most movies's sequels don't do as well as the original...or you'd have to do a tv series.
*grins*
THE METHOS CHRONICLES!
~ana