why is academia left-leaning ? 

I haven't watched this video by the very awesome Adam Something, but I can attempt a two line answer combining an old adage and a T.Kaczynsky idea -

- those who can, do ; those who can't, teach

- the left is about people who cannot 'do', and therefore have to do what they can to destroy what the 'do'ers have achieved

of course, the flip side is that welfare is seen to have worked in many cases, as opposed to the bootstrap prescription given to the disenfranchised

I love the 'Dubai is a joke' video by the same guy.  

Adam something comes from eastern europe, with a good dose of germanic thinking.