Because good idea in theory != good idea in practice. Showing that this actually works in practice (albeit on an isolated incident) shows that the bug is dangerous in practice, not just theory. Look at all the research in timing attacks etc on TLS, some of which are theoretically feasible, until you consider real world possibilities of remote servers, such as "Their ISP is fiddling with routing so I have varying latency", or "They're using different server configurations and I don't get connected to the same one every time". This has been PROVEN to steal someones private key, which is worse than giving someone the keys to your house, It's like giving them a blank passport with your name on it, letting them put their photo on it, and with that taking your car keys and hosue keys, and everything that identifies you.
Luckily, the fix is easy, just upgrade, revoke, and force password changes for everyone.