Since everything regarding space is so frickin' expensive (launch, engineering, software, manpower, training, materials...), the opportunity costs are simply too high for the expected short- to mid-term returns. You may ask yourself: what about the Apollo-Program? The 60`s spacerace was approved by politicians for signaling-purposes in competition with the USSR; such an external factor is currently absent.
With that said,on an optimistic note: a lot of people have held onto the dream of the final frontier and are exploring possibilities to reduce esp. the launch cost, eg. by starting rockets from flying boeings.