I feel that the Giygas fight could actually have functioned as a sort of "marketing hook" for the game in the internet. (Not intentionally, obviously.) I think that things such as "Top 10 Scariest Things in Nintendo Games" lists could have actually served as many people's introduction to the game. And since some would look into it more and some wouldn't, this is probably why there's a focus on it, it's pretty much the only thing they know about it.