Because we need another Planet of the Apes after Tim Burton's horrible remake. I've still got the bad banana peel taste in my mouth after that one. Apparently, Fox disagrees with me, as they have tapped Rupert Wyatt to direct a planned prequel to Planet of the Apes. The title of the film will Caesar, and is being written by Rick Jaffa and Amanda Silver(The Hand that Rocks the Cradle).
The story is said to be more sci-fi and socially thematic than Burton's film, dealing with hyper intelligent chimpanzees created by human scientists. It is not a remake of Conquest of the Planet of the Apes, as some have previously speculated. It's a project that has actually been in the works for a couple of years.
This sounds like a horrible idea. I'm not familiar with Wyatt's work, since his only film of note is The Escapist, which I've actually heard good things about but I haven't seen it yet.