Because HitFix can now exclusively report that Disney has begun quietly telling cast and crew to set aside a major block of time in the very near future so they can shoot "Pirates 5" and "Pirates 6." And, yes, once again, they will be shooting them back-to-back as one giant film, and then they'll release them as two films.
Is Pirates 4 even done with production yet? Is Johnny Depp even on board? Without him 5 and 6 are going to bomb and require the studios to ask for a government bailout.