Thiel's program is designed to generate startups. It should not be surprising that it generates more startups than other programs designed to reward endeavors other than generating startups.
Meanwhile, whose interests are served by future unicorn founders being plucked away from the liberal arts, or from the connections and experiences they would’ve had in college with people very unlike Peter Thiel?
In comparison to that, Thiel's success rate looks a bit more ordinary.
Rhodes scholarships etc on the other hand are a fair bit more successful at generating academics and researchers and mid level managers from backgrounds that don't usually become mid level managers, because that's what they're for