It's an interesting question and I'd have to think more about the specific question of the nature of academia promoting Leftism. But I do have some thoughts about the surrounding issues.
For one, you have to look at the people going into academia. Overwhelmingly Middle Class. The wealthy have business connections and opportunities outside of it. The poor used to have little opportunity to go and the effects of easy loans (not so easy to pay off) hasn't yet percolated through to changing the general demographics. So the make-up of academics is overwhelmingly drawn from a demographic that has been riddled with the basic indoctrination of Leftist principles for some time. Wokeism is effectively virtue signalling by a class of people largely uneasy with their, and I can't believe I'm actually going to use this word for once, privilege. The wealthy and the moderately wealthy have always indulged in demonstrative demonstrations of generosity and gratuitous largess from the Pharisees onwards. It's a pacifier to the masses. The wonderful refinement of wokeism is that you don't have to actually give wealth anymore, you just have to signal that you have the right beliefs. Okay, okay - you do have to give money but not to people who actually need it, just those grifters who "represent" them like BLM. And that's just for companies anyway who write it off against taxes. If you're not a company then you just run a fund to raise money (and take a cut for "travel" and "administration"). My point, anyway, is that academics are drawn from a class of largely woke people. There's a big selection bias going on here.
Secondly, what is the purpose of academia? I mean, it must have some purpose, right? Well if it's maths, biology, whatever, the purpose is more directly related to industry. And we can see that these subjects are less infected with Leftism. Or at minimum that you can be successful in them without being a Leftist. But what is the purpose of social sciences? Grievance studies, etc? It's paid polemicists. If you want to lead society to think a certain way, believe a certain thing, you pay your grants and academics will produce the studies and articles to back you up. You could pay the average academic history professor to dispute the Holocaust if you wanted and the only reason you couldn't find a professor to produce the papers you wanted is because they know taking such a job would cut them out of all future jobs. For less controversial subjects, it gets easier. Take environment money. Every academic in the last decade knows that if you slap an environment agenda on your research paper you'll suddenly get the grant. There's big money in biofuels and windfarms but for such a product you can't do TV advertising campaigns of "Buy Mr. Sieman's Wind Turbines for all your energy needs. Your neighbours will envy you!". No, academics are the marketing department you call on when you're pitching to govenments.
So basically, is there a financial reward for these social scientists and grievance studies professors to "believe" what they believe? Totally - modern identity politics is a way of diverting the energy that would go into class politics. It has a very valuable social function - if you're rich.
Finally, it's self-reinforcing. Academics are the modern priesthood. Remember how the third son would always be sent off to be a priest? You get a bunch of people who don't have immediate practical value (apologies to my Arts and Humanities doctorate friends who are lovely people) and deep down know that they're not earning their own way but subsisting on other's generosity. Nobody likes to feel useless. They have to believe they have purpose. And preaching Leftist politics gives that sense of purpose. If you just teach an understanding of history, do you feel empowered? No, not unless you actually love History and I don't think most academics do love their subjects anymore. But ah, if you teach someone to go out and bring progressive enlightenment in the world as a culture warrior, then you're Aristotle reborn - what a rush!
None of this really answers your initial question which I still think is worth exploring. But it provides alternate explanations for the outcome you've observed.
