GitHub organizations (or GitLab groups, Bitbucket teams, etc.) are a nice tool to attract individual projects, and drive their development under a common umbrella to reduce redundancies and improve consistency between them.
I want to share my positive experience in this regard: I started to develop RecurrenceAnalysis as one of those “hobby projects”. Time after I was invited to join the JuliaDynamics organization and move my package there. This started a fruitful collaboration that helped to improve the package, providing it with much better documentation — consistent with all the other packages of the organisation, a narrower focus — moving some features to other packages (e.g. DelayEmbeddings), and better performance.
Regarding the question of “more packages” vs. “better packages”, I think that JuliaDynamics is again an example of this not being a real issue: that organization has a set of packages dedicated to particular tasks, and also the DynamicalSystems library that installs them together.
As others have already said, this does not happen magically; it is necessary one person (or a few) that leads and coordinates the collaboration — in this case it is @Datseris, whose excellent work I want to praise. In my opinion this is a success story, that may be used as an example of how to move towards such a leaner ecosystem. Perhaps George might share his experience, and tell what resources he has needed to achieve this, good practices, etc.