[devishard]

I don't know how you came to that conclusion.

My assumption is that they're selfish assholes who want to successfully launder stolen Bitcoins. Holding on to Bitcoins and laundering them through tumblers gradually would allow them to do that. But it seems like every time a thief steals a large amount of Bitcoin, they try to put it through a tumbler all at once or come up with some other scheme that doesn't work to launder it all at once.