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.

Right! This is a criticism of philosophy in general, and I think it's very well-founded. In particular, the incentive structure of professional philosophy tends to encourage this kind of abstract theorizing that's disconnected from real-world social ills. Any kind of "applied" philosophy (applied ethics, applied political theory, philosophy of any particular science, &c.) is very much treated as a kind of second-class research project within the profession, and inferior to "pure" metaphysics & epistemology. My own area of specialization, foundations of climate science, is no exception here: making contact with concrete problems, or engaging with actual scientific work, is always seen as less prestigious than working on pure logic-chopping abstract theories.

I do think you're right that you're not incredibly likely to find "practicing" Marxists at the upper echelons of tenured R1 philosophy (though there are a few prominent exceptions that I'm aware of, and it still seems a bit more common than it is in most other disciplines). However, there's a vast underclass of (let's say) lumpenprofessoriat members--adjuncts, community college professors, non-tenured lecturers, and so on--that is, in my experience, extremely likely to endorse and be engaged with Marxist thought. As you say, this is almost certainly down to material conditions, at least to a great extent. I do think that a background in philosophical reasoning can help with though.