@ItsJustCurtis op probably meant libertycity.net. that site scours the web for mods, typically updates them, and re-uploads them. They host many abandoned or "lost" mods on their page as well.
I don't think much can be done to prevent that from happening. Technically speaking, modders do not own their content if their source material is owned by someone else, unless the owner of the source material explicitly gives them ownership of their creations.
Unless the owner legally backs the content creaters, "owning a mod" is a fallacy. Rockstar doesn't give two shits about supporting modders so it is a faith based operation running within the modding community and legally speaking, any person can upload any file, anywhere and at the end of the day, they are actually only infringing on the rights of Rockstar by doing so.
Edit: the models are a slightly different story if made from scratch. I was mainly referring to the coding aspect of mods. However, it is kinda hard to take ownership of a GTA V mod created from bootlegged Forza models js 🤷