Many of the producers of the plugins are against a central repository for reasons you can guess; licensing and revenue generation. One annoying part of working with various plugins is the companies tend to have gatekeeper applications the user needs to interact with to get plugins authorized and installed on their system.

You will find applications like this one, https://www.pluginhubapp.com, show up frequently to try and manage this complexity. I am in no way at all recommending this application, but it is an example. This application does ship with all of its python code in the app under (possibly a mistake) so you can see the hoops they have to jump through to try and make their system work.