Why have the Americans developed space shuttle according to the passage?

Ever since the Apollo moon landings, the idea of human expeditions to the Mars has come up repeatedly as the kind of grand adventures that would give focus, purpose, and inspirational lift to the space program. But confronted with the cost — estimated at $ 150 billion last week — presidents starting with Richard Nixon and others have flinched and resorted to halfway measures like the shuttle.

The new nepotism operates not from the top down but from the bottom up: it is voluntary, not coercive; it springs from the initiative of children, not the interest of the parents; it tends to seem "natural" rather than planned. Although no nepotism in the classic sense, it is rightly nepotism because it involves exploiting the family name, connections, or wealth. The method may be different, but the result is much the same.