I think it's just because they use elements from multiple different games, so it's neither completely new (therefore no new title), nor is it a direct adaptation (therefore no existing title), but a mix of all the games, therefore just "The Legend of Zelda". Just my understanding.
Oh god. People are going to say stuff like this aren't they 😦
The same jokes we've been making for forty years... people are going to try and make it "a thing" for real aren't they?! 😱