James Gunn's answer about it being a car sold to your neighbor though isn't quite right. It's really like Fox is a renter with a lease for 8 years. We don't know for sure that this is the length of time that can lapse without them putting something else in production. But the pieces do sort of fit.
Fox went into production in 2014 with Trank's film and Rise of the Surfer came out in 2007. Ike Perlmutter gets all crazy (allegedly) about the Fantastic Four around the time is announced that Fox is filming a Fantastic Four film. Fox was on the verge of letting the rights lapse when they made their slap dash film, with an est. budget of 120 million. Quite frankly it sure looked on the cheap side to me.
With Daredevil, Fox did let the rights lapse back to Marvel and that's why they get to make a Netflix series with him. Rumor was that Marvel was trying to work out a deal with Fox to keep Daredevil if they could have some Fantastic Four characters back like Galactus, the Surfer or possibly Doom.