@Predator is talking here
Because established directors/writers are not hired guns, they work on movies they want to and that's rarely sequel X in a franchise. Even if you drop insane amounts of money to hire them, they will half ass their way through it just to fullfill the contract.
John McTiernan and Jim/John Thomas as writer were nobodys at the time they made Predator. Shane Black was an established director and even more so as writer (he even had ties to the first Predator) and yet his Predator movie sucked hard.