In 2011 there wasn't an actual flash crash, it merely went from a quick rise to $31 back to $18 in the timespan of a few days, after which there was a major hack at MtGox which knocked it offline for a few days.

There was a lot of bad press surrounding this, and people lost confidence - also, there was much less liquidity in the market then, and barely any places to spend any coins. Hardly any bad press now.