It's the simplest way for github to archive a system which seems to work well in general.

Then they throw it at the community and hope that any rough edges/problems are overshadowed by the hype around it and by cool thinks people do with it. Then they can slowly incrementally fix it with "live" feedback.

Ironically while this might seem bad long term it can potentially lead to a better end-product from both the view of github and the users.

The only problem is that you run at risk of ossification, i.e. you no longer being able to fix a problem because to many rely on it being that way.