I think, because that list will only contain integrations that can be set up via the UI (i.e. using config flow). I’m not saying it can’t be made clearer. Just saying what seems to be the case.
My use case: someone mentioned an integration and I went to config/integrations to find it. Not there. I don’t add integrations every day, so I assumed maybe the integration was discontinued.
It would have been helpful if at the bottom of config/integrations there was a simple note saying: