Money laundering 101: breaking the transactions up into smaller and smaller amounts making them more and more difficult to track
I'm curious if Zhao discussed with some of the mixers' owners to block those funds. That would be an interesting move. Then the hacker may end up with a pile of Bitcoins he cannot ever use, unless he'll start sending to unsuspecting fools really small chunks. Or simply with the money seized by the mixer and returned to CZ.
I think some exchanges have notified CZ already that they will block those addresses, but I don't know if he has discussed this to some known mixers to block it as well. But it's going to be difficult to get their cooperation though. Anyways, there are a lot of blockchain forensics right now and I'm sure their hands are full trying to track everything down to the smallest amounts and where it goes.