If they don't know what they are doing, then why are they the leaders?
Because they have access to the biggest club. They claim Earth's resources as their own, and can back that claim with (outsourced) violence, so everyone else either obeys or starves. Actual competence in using those resources is irrelevant.
Besides, it's not like they're actually in charge - market logic or the "Invisible Hand" is. They have some leeway in interpreting its will, and particularly competent ones can sometimes even suggest a course of action, but ultimately they are just pampered slaves.
An executive's job is a purely ritualistic one: they're posing for the public while interpreting orders from high. The only real difference between them and, say, an Aztec high priest is that the Invisible Hand wants its victims starved rather than TempleofDoomed, which is less messy. Well, currently they victims are mostly just made destitute rather than outright killed, but born-again InvisibleHanders are working hard to change that.
Of course, the real problem with this scenario is that the Invisible Hand is not self-aware and can't think ahead, so the end result is that no one is in charge. Explains a lot, eh?