anime titles be like

Backstabbed in a Backwater Dungeon: My Trusted Companions Tried to Kill Me, but Thanks to the Gift of an Unlimited Gacha Got Lvl 9999 Friends and Am Out for Revenge on My Former Party Members and the World

This is a legit title of an anime currently airing

I'm actually cool with this. It tells me all I need to know, although a shorter title like "generic pseudo-fantasy schlock with video game mechanics #3456" would've worked as well.
- Its also is exactly as trashy as it sounds :D
I think that's the literal translation of the Japanese title. They shortened the English one to "My Gift Lvl 9999 Unlimited Gacha: Backstabbed in a Backwater Dungeon, I'm Out for Revenge!"

It's missing the "I was reborn as a [...] in another world" part.

The Analyst: Reborn into Another World to Provide A Discourse Addressed to an Infidel Mathematician: Wherein It Is Examined Whether the Object, Principles, and Inferences of the Modern Analysis Are More Distinctly Conceived, or More Evidently Deduced, Than Religious Mysteries and Points of Faith, and Mathematical Formulae Make me Overpowered??? A Slow Life Adventure in the Dungeon
How's that?
- 🤌
Silliest I've seen so far: Reborn as a Vending Machine, I Now Wander the Dungeon
- Well then I've got some piracy to do!

I’ve wondered about this for a while and assumed it was AI slop by production companies spitting out whatever content en masse.

Then I came across a youtube video where they explain the reason is those shows are adapted from written stories on some site in Japan. Think Wattpad or AO3 (but not fanfic). And since there are so many stories posted there, writers title them that way so readers immediately get a sense of what the story is about and hopefully choose it to read. So the anime adaptation ends up taking on the long-ass title.

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" 😅