Screaming on cue is hard.Acting can be difficult. Screaming can actually be worse. It's hard to scream convincingly when the proper motivation isn't present. It also isn't advisable for all performers, as you're probably going to need several takes and very little strains the vocal cords like extended screamfests. Horror's scream queens are professionals and even they can wind up whispering for weeks.
And so the creators will turn to the sound effects vault, which has a selection of screams waiting for use. And the count on 'selection' is 'about fifteen'. Because the screams are effective, cheap, and in every single vault for even the smallest studios, they get used over and over and over and over and pretend I just kept writing the words 'and over' for roughly sixty-two years, which is the current lifespan-to-date of the most popular. It can be heard everywhere, coming from throats which never should have produced it, because it's convenient and cheap -- especially cheap. Also cheesy, because audiences willr recognize it and groan. But directors grew up on that cheese, and some will use it on purpose just so the next generation gets a taste...
Private Wilhelm has been screaming his death for sixty-two years.
http://tvtropes.org/pmwiki/pmwiki.php/Main/StockScream
And he was the second to use it.
Really, what was wrong with Sheb Scream?