Right now the economy and various wars seem to occupy the public's attention, and the politicians are campaigning on those. As well as negatively attacking each other.
If the public cared about space, or science, or a cure for cancer I believe the candidates wouldn't shut up about them. As it is, in addressing the topics they would inevitably irritate a significant number of people without attracting a correspondingly larger number.
It's no-win until Joe and Mary Six-Pack are interested.
Now if one of 'em discussed the science behind restricter plates on NASCAR engines and suggested removing them, they would gain all manner of votes without offending the vast majority of folk who don't give a rip.
Arf