The people that build the best stuff are the people who build things they themselves would want or use.  For me personally, I've never thought to myself "holy shit I wish I had spaceship to go to the extremely hostile environment of mars in an extremely slow manner and then probably die when I get there".  Maybe if Earth was populated by a few more Jews and noggers, but we haven't reached that point yet.  

I'd also have to be researching something faster or more efficient than a liquid or solid fuel rocket for it to be worthwhile.  Then you have to factor in tiny space debris being like an atomic bomb hitting you when going fast and you get to the point of needing something resembling a planet to strap rockets to in order to not insta die.  And then you realize you're already sitting on a giant spaceship traveling through space anyway.