Don't these providers need to be registered somewhere? It should be easy to reach them and provide with either code generator software or even printed one-time codes for database addition.
Why use a centralized model? Allow users to subscribe to a data source so that any entity can push their own dataset.
This is also important because it keeps the framework usable under a variety of adverse and unusual circumstances. An aid organization operating in a disaster zone or impoverished area could make use of such a framework without needing permission from a higher authority or even reliable internet access to the outside world.
Because it can abused. The easier you make it upload, it also allows bad actors to upload invalid data to cause people to go into quarantine unnecessarily. It only works well if you can trust the data, so I think it should error on the side of validating the data instead of openness.
In an open model, the extent to which abuse is possible would be determined entirely by the authentication requirements (or lack thereof) imposed by the entity operating the server the user selected. That being said, another commenter linked to a set of specifications (https://news.ycombinator.com/item?id=22836871) which seem to indicate that (at least on iOS) the data source is determined entirely by an app that the user chooses to run on top of the framework.
This is also important because it keeps the framework usable under a variety of adverse and unusual circumstances. An aid organization operating in a disaster zone or impoverished area could make use of such a framework without needing permission from a higher authority or even reliable internet access to the outside world.