I think the centre of the matter lies with the fact that no one wants to pull the shuttle and spend shuttle money on developing a new craft, because they're worried that if they pull the shuttle, the money for it will disappear, rather than being invested in new tech.
$5 billion a year supposedly, would pay in reasonably quick order for a modern re-usable launch vehicle, it just needs someone to grip it and their chain of command/budget managers not to take the money off them while they try...