Such attack is not cheap, and whoever was behind it spent what he had, at least for now.
DDOS attacks usually use a botnet (made out of many hacked computers). That's actually quite cheap to do, and very expensive to fight off.
Bitcoin mixing is big business, and some use criminal methods to attack ompetitors. It could also be used for blackmailing, I've seen that happen to Bitoin casinos in the past.