You’re correct that the big majority of philosophy academics are liberal. It’s good to bear in mind tho imo that philosophy professors are not the only people employed as philosophy educators or teachers and are far from the only people who have seriously studied philosophy, formally or informally. There are a decent number of Marxist philosophy PhD’s, not least from the combination of their experience of the labor market and the fact that they’ve had the time or priviledge to think critically about and ‘deconstruct’ certain key concepts that are essential parts of capitalist/liberal ideology.

The issue is not so much, imo, in areas of philosophy like philosophy of science, mathematics, language, logic or even epistemology and metaphysics. The more immediate issue is when it comes to areas like moral or political philosophy, or philosophy of economics. The biases in these latter cases are really evident and you are correct imo that when considering that social function they are largely serving as more sophicated mechanisms of ideological legitimation of liberalism or reformism. E.g. any western political philosophy department is going to be dominated by Rawlsians, i.e. the least politically relevant and most mind-numbingly boring political theory that was ever shat over the face of the earth. The most recent wave of Rawlsian thought is soc-dem in nature, looking at his late texts on ‘property-owning democracy’, meaning accepts to have soc-dem societies which ‘socialism’ has been reached by reform but in which there is still private property. Obviously even a slight understanding of Marxist theory dispells this idea as obviously incoherent. The reason it is still present is because it acts as a moral paliative that petit-bourgeois soc-dem intellectuals - who are intelligent enough to realise that contemporary capitalism is completely fucked up but are neither intellectually sophicated enough nor morally strong enough to correctly diagnose it or offer genuine solutions - can use to sooth their consciences.

That being said, you do often see a correlation with how deeply or seriously people are interested in philosophy and their interest in Marxism. The danger is that these people are often simply intellectual Marxists or Marxians with an abstract idea of politics. This is generally far from being entirely their fault, but it is a danger. In practice they are often interested more in abstract argument about certain ideas as opposed to the empirical and historical adequacy of Marxism as a theory of social reality.