At the time, hardware was bad and technology was not great. If they had to scale a single database, a single users table to hundreds of millions of people would have been impossible. Twitch's peaks were 20x that of other live video sites at the time. The site didn't figure out how to deal with this problem until later.
Dalton Caldwell and Michael Seibel on software hacks that don't scale. Companies discussed include Google, Facebook, Twitch, and imeem. Watch the first video on doing things that don't scale here: https://youtu.be/4RMjQal_c4U
Apply to Y Combinator: https://www.ycombinator.com/apply/