I have to assume the real explanation is one of these:
Monolith and WB wanted a sexy evil chick in their game. There’s no sexy evil chick in The Lord of the Rings, so they just picked Shelob because fuck it why not?
Michael de Plater has the same kind of interpretation of Tolkien that you get at least once out of every undergraduate lit class. Just some dumbass hot take that involves literally zero understanding of the text, but man, you just don’t get me, man.