EDIT: Downvoted, maybe I wasn't clear enough. Context is very important within a brand. If you start offering all types of videos on Twitch, the landing page isn't just going to show gaming videos any longer.
Also, iirc wasn't JustinTV polluted/tainted with a lot of dodgy re-streams of non-user-created content such as soccer?
It's a success story that they've managed to successfully cultivate twitch out of that and grown it up where they can now branch other user-streaming back from it.
I thought that they would spin off this Creative product in a new independent business venture so it won't clash with the established Twitch brand name or dilute it due to conflicting dynamics at play but this is Amazon after all and we're used to expect the unexpected from them.