I remain unconvinced. If github goes down, it goes down for everyones projects. If everyone ran their own servers, only one or two packages would go down at a time. So instead of 100% its like 0.1%. And since they're simpler, as per OPs comment, they'd stay up longer. So a distributed git, as it was originally intended to be used, is more robust than a single point of failure like github.

Perhaps githubs value is elsewhere.