The problem is Twitch infrastrucutre is not good enough to stream properly in many countries. A 1080p/60fps stream has only about a 6Mbit bitrate but in Australia will not work, even on a connection ten times as fast. Plus, without a special agreeement that only top streamers have, Twitch takes 50% of subscription money - I'm sure Google can afford smaller margins to lure streamers over.
The problem they will face is not that gamers are loyal so much as for many people "live video game broadcast" is Twitch, so people are unlikely to notice live streams if they're elsewhere. This is solvable though - most streamers upload their VODs to YouTube anyway so they can easily notify users when a streamer is live.