Because I cannot believe they're serious about this : re-making the original Buffy movie without Joss involved in any way, shape or form. Not to mention the idea that it won't have any of the characters or cast from the tv show either. Frankly, this is insane and smacks of people desperately trying to get the Twilight crowd on board.
After looking deeper into it, it looks like the original film director Fran Rabel Kuzui held onto the film rights way back then (which would explain the lack of the classic supporting cast we know and love - they simply don't have the rights to them) and is looking to remake/relaunch the film. So maybe more of a Star Trek success result prompting this then.
Currently, they're meeting with writers.