The article says that it looks like profile images can be downloaded insecurely. So now you can snoop on what people are looking at. And liking. Opportunities for blackmail, doxxing, griefing, etc., abound.
Also, attacks don't have to exist in a vacuum. As part of a larger suite of attacks, it appears to be a useful tool that can help build up a profile of somebody.
The answer when it comes to hacking is almost never "why". Rather, it's usually "why not".
disclaimer: let's have https everywhere and all that.
That said, you've described the 'why not'. All of the attacks you've identified are targeted and require significant investment. This opening doesn't allow for economically profitable mass-collection and exploitation (like say, grabbing credit cards or hacking into email accounts).
That's a bad line of thinking. Privacy doesn't work this way: there are a lot of things that you do every day and keep private even though they cannot easily be exploited. It's human nature.
Also, attacks don't have to exist in a vacuum. As part of a larger suite of attacks, it appears to be a useful tool that can help build up a profile of somebody.
The answer when it comes to hacking is almost never "why". Rather, it's usually "why not".