Converging and diverging paths

Winget is "everyone providing their software from their own website", literally, just not with the a web browser as frontend. It's not a central repository of binary packages, it doesn't do dependency handling, it's just a collection of recipes to fetch and run upstream binary installers.

When you install Firefox with winget it's literally downloading and running the same installer you'd have downloaded from the Firefox website. When you install git it pulls down the same all-in-one Git for Windows installer from the Git For Windows Github page that's linked on the Git website.

By contrast, Flathub really is a central repository of binary packages, accompanied by a central build infrastructure. Flathub hosts it's own binaries, and, apart from a few notable exceptions, requires packages to be built on its own infrastructure.

It's more than the Microsoft Store, even, it's really a proper package repository, just distribution independent with a focus on desktop applications, much coarser dependencies, and a few other minor technical differences compared to traditional Linux package repositories.

When you install an open source application from flathub you get, apart from. said exceptions, a binary that's hosted on Flathub infrastructure, built on Flahub infrastructure from upstream sources.