The site you're referring to is almost certainly Syosetsuka ni Narou, a free-to-use Japanese web novel platform, exactly like Wattpad and AO3 as you mentioned. Super common to have a very long title to grab reader attention there, because that's literally the only pitch you have for new readers on the front page or search pages.

And yes I wanna say almost every modern light novel has its start there. Publishers scour that site for potential new work all the time. It's not uncommon for you to be following a web novel there and then suddenly get an announcement about how it's being picked up by a publisher/editor for serialization.

The title sometimes gets slightly changed but usually it remains as is, and that's how it ends up on anime/manga.

I’ve heard sort of the same thing but not related to some website or whatever. Idk which is truthier, so I’ll add my understanding as well.

What I heard is It’s a category of actual books called light novels, they have a picture here and there but it’s mostly text, and they tend not to be super long. Think YA (young adult) books.

But what I heard largely agrees; that it’s such a popular category with so many options that that’s how they are named to give you a rough idea of what you’ll be reading at a glance.

Every writer of short stories knows the struggle. You can't name them all "Nina" or "Summer Camp" 😅