http://www.thebigmoney.com/articles/impressions/2009/02/17/spielbergs-lincoln-troubles

Steven Spielberg really is in trouble these days.

The extensive article on The Big Money talks all about the ins and outs of Spielberg's and DreamWorks' situation right now - and it's not good. If you remember, Spielberg's other big passion project, Tintin, also had trouble getting funding. Back in September we reported that Universal told Spielberg that they would not be funding Tintin, although Paramount and Sony eventually came to the rescue. I'm not sure whether these issues relate to financial agreements he's trying to arrange, or because the studios aren't so sure of their potential.

Spielberg doesn't come cheap.

You want his services,he's going to want a nice chunk of the profits on top of whatever fee he charges as a director, producer, etc, not to mention what Dreamworks would make off the deal.
So any studio is going to hope like hell the movie makes hundreds of millions of dollars just so they can turn a profit.