Yup, to expand on that I had a chance to chat with someone at Justin.tv and they said a thirty second ad pays a lot more than the cost of serving video for an hour. iirc this was around 2009 or 2010?
Also, iirc even through 2014, my friends who played League of Legends (lol) used to watch stream on VLC instead of directly on the website on Twitch. The consensus was for lol, 720p60 was preferable to 1080p30.
I don't think Twitch got where it got because of technical prowess. If I had to guess, it was just lucky being first. It would be interesting to hear stories from the people at YouTube. Why did it take them so long to add live streaming?