We're governed by incompetents because we elect incompetents. We elect them because voting has become more of an emotional/cultural decision than a logical one. And this is largely because the big problems everyone could agree on have been solved - we're not under threat of attack from other countries; social security and medicare and other social welfare programs have taken care of much of the visible suffering in society; regulation has taken care of others.
As a result we're left with issues that are harder to pin down and harder to solve (why are medical costs so high? how do we legislate on privacy?) and issues that have been turned into culture war elements by cranking up the emotional component and discarding the evidence and effects (abortion, Brexit, the wall, etc.)
Also, I'm tempted to say that blaming this on boomers is a causation/correlation error - I'd look at the changes in media, starting with the TV debate between Nixon and Kennedy. It feels like since then, policy has mattered less and less, and appeal has mattered more. TV news feels like it has become ever more emotional over time - Fox appeals through fear, MSNBC through anger/frustration, CNN through surprise (breaking news alert!)