When you're writing a SF novel, you have none of the budgetary and practical constraints that hinder SF TV shows and movies. You can have a giant space squid eating the Moon if you want. There are literally no constraints — except for the need to make sense, says Monster author A. Lee Martinez:
Just because you can write something, that doesn't mean you should. The burden of the novelologist is self-control. Not just the self-control to make yourself write at a reasonable pace, either. I'm talking about the ability to take a good idea and not use it. Movies and television have a natural control mechanism. They have budget and time constraints that make some things impractical. The original Star Wars films are infinitely better than the prequels, and it's not because of the writing (which has never been the movies' strong point). It's because the originals were made with a budget, without CGI. Just because someone could imagine it that didn't mean it could appear on screen. And that made the original Star Wars trilogy stronger versus the prequels, which are overindulgent, so crammed with visuals and ideas that none of them really get the time they deserve to get us invested.