There are several rumors as to why this would happen, number one being money. It costs money to cut, re-shoot, edit, etc. The Weinstein Company has had a bunch of flops over the last two years, most notably Fanboys, The Long Shots, etc. I'm a bit divided on this one. There are three hour movies that need not be, i.e. every Speilberg movie, and then there are those who need the entire time to tell the story, i.e. "The Dark Knight".
I also believe that it is the artist's choice to do what he wish with the picture. Tarantino, hate him or love him, is an artist and should be allowed to work his magic anyway he see fit. But the other side of me sees the potential problems in a three hour picture. Less showings at theaters during any given day, 90 minute action flicks that make much more money, and marketing. There are movies that pull it off like the 'Rings' trilogy, but for the most part, it's very difficult to have a viable three hour film.
