I'm seriously committed to climbing down from the ivory tower of academia and explaining science to people as much as possible.
The first reason is to follow a democratic ideal: people are the ultimate employer of scientists. Therefore they should be informed about where their money goes. And they should also be put in a position to make the best possible choice when, indirectly, they will have to decide where their money goes.
The second reason is personal: I'm passionate about what I do, and I can explain to you why! There's no need to to be trained in physics and higher mathematics to understand what's cool about my research topics. If one's research cannot be explained to a sufficiently smart layperson, then maybe it's not that interesting.