When you say “liberalism”, what are you talking about specifically? If you mean liberalism as in like, the enlightenment, the foundation of modern society and in the context of “liberal democracy”, I’d say that’s because most historians that you are reading are born into liberal nations where things like a market, freedom of speech, freedom of the press, and due process exist and are valued. If you mean liberalism as in American left-wing politics, I’d mostly disagree with the premise of your question.

The more I've entered into the social sciences, the more I've understood the first chapter of Bourdieu's Practical Reason. The chapter is a brief exposition of "social space," a plane in which cultural practices and positions are located and defined by their relations and differences. It is also, explicitly, a critique of what he calls "substantialism:"

The "substantialist" and naively realist reading considers each practice (playing golf, for example) or pattern of consumption (Chinese food, for instance) in and for itself, independently of the universe of substitutable practices, and conceives of the correspondence between social positions (or classes, thought of zrs substantial sets) and tastes or practices as â mechanical and clirect relation [...] The substantialist mode of thought, which characterizes common sense - and racism - and which is inclined to treat the activities and preferences specific to certain individuals or groups in a society at a certain moment as if they were substantial properties, inscribed once and for all in a sort of biological or cultural essence

What does that mean? Bourdieu gives the example of golf. At one point in time, golf was a sport limited exclusively to upper classes. Now, every other public high school has a golf team. There's nothing intrinsically, "substantially" upper-class about golf; it's position can change according to the society that plays it. That quality is based on difference, it's relational, not innate. It has a position in social space that is a certain distance from other things, in a certain direction.

Bourdieu then makes the jump from the mundane to the highly political/theoretical: "classes," as had been understood by Marxists, likewise don't exist. There's nothing substantive about the "proletariat." If people are plotted, it represents a "region" of them that are closer together and thus more likely to be more similar in certain attributes. What defines the group is location in social space relative to other classes.

More simply, you couldn't have a society with just one class (that would render it classless). If all my LEGOs are red, why would I sort them by color? Or imagine trying to demonstrate the concept "red" with your monochromatic bricks. It's nigh impossible- but becomes easier with each color you get. Relational, spatial definitions are based on difference, or what Bourdieu goes on to describe as distinction: things become socially relevant when we actively distinguish them. The material, substantial difference between loose blue jeans and tight black jeans is meaningless- because we actively distinguish them, wearing either pair suggests something different.

Eventually, the argument in later chapters gets to what, for me, is essentially a statement that "the state" doesn't exist, and that a lot of the scholars before Bourdieu, e.g. Marxists, structuralists, etc., had overemphasized it's role. Think about it for a second: what is the US government? Is it a thing? I like to call the phenoma "state-thinking:" there's a state because people think and act as if there is. If people suddenly stopped acting as if the state existed, would it really exist? We obey a police officer Jane and not random drunk Joe at the bar because we distinguish them: Jane has the endorsement of the government and Joe has a 0.1% BAC.

Hence the "theory of practice:" instead of looking at these "things," we should look at what people are actually doing and how those actions, that practice, creates these "things."

For anthropologists, this is an important text that adjusts for some of the short comings of the writers of the '60s, '70s, and '80s. It reminds us that we can't isolate a cultural practice as some kind of naturally bounded entity, but understand what it as what it actually is: a practice. If I want to study Chinese food, I can't pick food that's "Chinese," follow that, and insist that, wherever it goes, it's still "Chinese." I have to study the food that Chinese people make, whatever that may be and however much it goes against any tidy definition. Likewise, taking, say, a set of curative rituals practiced by a Quchua town in Peru and studying those, describing those, and, in essence, isolating them as the object of study, can only tell me so much. What matters is how people do them, and how they act in response to this acknowledged practice.

For critical theory/social sciences in general, these principles encourage us to question how substantive out categories are: "nations" or "ethnicities" or "races" or "states" or "languages" or "kin-groups" or "genders" or "fans of Real Madrid" or "actual fans of Real Madrid."

Has every historian read Bourdieu? Of course not. Plenty actively hate him. But there's something about studying people foreign to us, be that in physical space, cultural distance, or in time, that makes us question the realness, the substantiality of a lot of modern institutions. That things like nationality, ethnicity, or government have "substantial properties, inscribed once and for all in a sort of biological or cultural essence" is crucial to much of right-leaning politics. We history folk are a lot more likely to question that, and there's a lot of right-ish stances that require a substantialist understanding of nationality, especially, to make any sense.

This has led to, at least in my anthropology department, a lot of people who would rather not identify as left or right, and who often question the tenants of most of the West's "left" parties as much as the right does. This is most notable with things like identity politics, something that the American right loves to hate on, but that most anthropologists, and most actual Leftists question just as much.