Quoted from BC_Gambit:
That is just preposterous and amazing for a multi billion dollar franchise, where a trilogy is planned from the get go. I mean how does something like that even happen, unless writing is about the last thing on your mind when milking your franchise to death?
It happened with the prequels also.
Quoting George Lucas:
“Ya, they’re already building sets! God, help me! I’m gonna have to start this script pretty soon!”
Happpend with POTC 2 and 3 also, they were writing their scripts up while filming was already in progress.
Hollywood's a mess I guess.