From my memory the profits from such attacks were remarkably low. In particular it's very striking that the hackers who compromised JP Morgan couldn't find anything more profitable to do with that access than send basic scam emails to their client lists.

Your comment makes it sound like stock markets were manipulated by hacking the companies that issued the stock. In one of your stories brokerage accounts were compromised and used to pump penny stocks. In the other someone hacked a few companies that distributed press releases to get early access to them and traded on the information. Stocks weren't even manipulated in that case, they simply placed trades based on how they thought the market would react to the news. That was a targeted attempt to get information, not a destructive attack on the entire company network.