Just to play Devil's advocate...
Perhaps Sony is taking the "maximize shareholder revenue" avenue. What is their financial loss for months of PSN downtime? A few people switch to xbox live? They have to provide a few free accounts?
For their other hacked services, they can simply shut them off as failed experiments, fire all the developers, and save even more money.
Because there is not some huge fine for leaking all the credit card information, this doesn't affect Sony at all, financially. But allowing people to run Linux means they may take a loss on a lot more devices (and if they don't take that loss, people will buy Wiis or Xboxes instead), and it makes piracy a lot easier. If piracy becomes too rampant, developers will stop targeting the Playstation, killing the entire line of business.
So while it makes them look dumb to keep getting hacked over and over again, maybe it isn't hurting them at all.