Because nobody will take security seriously until something bad happens?
Well, no. It's because the document wasn't actually sensitive. Anyone who actually might want to cripple our infrastructure already knows how to do that, because they have access to satellite imagery like everyone else. Also, not being complete fucking idiots, they know how to read the reports that all corporations are required to file which include information on things like new construction projects, including their function and location.
The truth is that most U.S. cities get their power via just one or two links, and the locations of those links are extremely well-known. If anyone wanted to cripple our infrastructure, they could have done it already.
Now, the fact that our power grids are particularly sensitive to a physical attack, that is a factor of nobody taking security seriously. But then, that's because efficiency is more important, because there are so few actual threats to security. As it turns out, one guy in a pickup truck can cripple a city's ability to function. You don't think that any enemies could muster those kind of resources? Nobody is even trying.
On the other hand, there's lots of good reasons to secure our power infrastructure from domestic criminals. But I'd prefer to reduce the production of those criminals by overhauling the system to reduce or eliminate the poverty industry. It's better to make the world a better place than to make the world a safer place for shitheels to be shitty, which is where focusing on defense gets you. Let's focus on cooperation.