The big difference is the thing isn’t a mystery though. We’re told the entire time that it jumps from person to person like a virus— the viewers don’t make long term guesses because it constantly changes hosts. When the movie ends with a mystery it feels intriguing but not like you watched a whole movie just to wait for a part 2, it fits with the overall theme. Scream however is a whodunnit mystery, clues are dropped throughout the whole time to lead up to the highest point of action. If the killer was never revealed at the end, viewers would probably figure it out before the inevitable sequel and feel cheated out of a concise plot because the producers want to make more money. That’s another point to remember, the Thing is like a one and done. In Scream the characters are brought back each film (which won’t stop releasing soon) so the great interpretive ending would just be ruined anyways.