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.
Because that's definitely one reason why some developers still don't use GitHub.
Take a look at this request which has been open for years and remains unfulfilled:
https://github.com/dear-github/dear-github/issues/74
Is there a reason that such incredibly basic functionality doesn't exist on GitHub but does on all your competitors' offerings?