The obs-studio Fedora flatpak exists because the maintainer (yselkowitz) decided to make one. Ditto the few hundred others that exist - https://src.fedoraproject.org/group/flatpak-sig . Some of those are dupes of flathub, some aren't. Of the ones that are dupes, in some cases the flathub build is 'official', in other cases it isn't.
and yeah, yselkowitz created a lot of them, most of which are very simple - it's not really a lot of work to create a flatpak when there's an existing package, the definitions for most of them look like https://src.fedoraproject.org/flatpaks/bless/blob/stable/f/c... . Kinda the point of Fedora flatpaks is that you get a lot of the work done 'for free' in the package build.
I don't know why he decided to create all of those, maybe the idea was to try and create a critical mass of stuff so it would be kinda viable to get all your software from Fedora flatpak repos the way you can get all your software from Fedora RPM repos, if you want to.