We know that the account was compromised because they reset passwords on some websites. We also know that they account was never "deactivated". Most likely it's Satoshi's FPGA order. Just because you have lots of bitcoins doesn't mean you would buy 1000 FPGA's. Why would Satoshi want to mine many more Bitcoins when he owns 1,000,000 of them? He was just tinkering as a hobbyist.