We've wanted to make this change for the last 18 months, but needed our Enterprise business to be big enough to enable the free use of GitHub by the rest of the world. I'm happy to say that it's grown dramatically in the last year, and so we're able to make GitHub free for teams that don't need Enterprise features.
We also retained our Team pricing plan for people who need email support (and a couple of other features like code owners).
In general we think that every developer on earth should be able to use GitHub for their work, and so it is great to remove price as a barrier.
I wasn't aware of SS13, and will look into what happened there. Content moderation at GitHub scale is hard and sometimes mistakes are made.
This is completely fair, but lack of transparency makes it significantly more frustrating.