Lindelolf wrote in a bunch of unanwsered questions and pissed off to leave someone else to clean up the mess. It's not surprising they can't find a writer who can be fucked to tie it all up properly.
What's really fucked up is that James Cameron and Ridley Scott originally approached Fox to make Alien 5. James Cameron wanted to write, with Scott directing and Sigourney Weaver starring. The idea was to take it to the Alien homeworld. Fox turned down the proposal because they wanted to make an Alien vs Predator film. Neither Cameron or Scott were interested in that so they walked away and the whole deal went down the toilet. So to replace them they got Paul wet shit Anderson to direct his vision of AVP.