>Because the astronauts and their training are themselves a valuable asset.

Magellan, Hudson, Cook and a litany of others were certainly not cheap cannon fodder. Yet they were allowed to take on immense personal risk and risk to their crews, above and beyond the standards of the time because it was deemed worth it.

There is a fine line between reckless and acceptable risk. The cost of such endeavors absolutely pales in comparison to the long term potential for wealth creation for the rest of humanity by making the resources of other planets reachable.