Twitch was one of the earliest video game streaming services, being spun off from Justin.tv. As a result, it's steadily built a large community, further boosted through e-Sports related partnerships. As a result, there are plenty of streams to watch at any time.
Since Twitch implemented an up to 60 second delay for all streams on its service, this has become a notable feature. This issue is particularly important for streamers who interact directly with their viewers.
As streaming is curated, rather than open to any broadcaster, the amount of content is severely limited. Azubu isn't a place where you can watch 'Let's Play' videos, blind runs, or casual races and speedruns.