I think it’s more a correlation than a causation. It is not that LGBTQ are better at running companies, but that a company that never promotes or advances them is almost certainly not promoting based on capability and appropriateness for a position.

More likely it’s promoting based on personal relationships and connections, an old boys network. Which leads to people who are less qualified, but better connected, ending up up running things.

Counter to what the anti-DEI people will claim, diversity in a company is the result of hiring the best qualified people, a company that lacks diversity is a sign of poor hiring practices.