Why did this never happen?

Some movies deserve a sequel, so why did some of the most popular slasher movies of the 80's never get a sequel? We may never know. I mean you had so many sequels for movies that never had a following like these films. What they could have done with these franchises, we will never know. Just to show you how bad fans wanted to see the return of these iconic killers, here are some images I found online. Let me know of any I forgot.