On the other hand: Exchanges make money with every trade users make. It would make sense that they prepare themselves at high traffic times, downtime will only cost them money.
I'm with you, but it could be the case that they legitimately were not prepared for this as well. After the $10K limit was reached, the popularity of bitcoin skyrocketed like I had never seen before. People around me who had no idea what bitcoin was until then, started talking about how one could obtain it. If even a fraction of such people signed up on exchanges, they may have overloaded their backend systems.