But they do have to “craft a class” to some extent. An obvious example is athletic recruiting, but some schools are consciously thinking about populating other extracurriculars, like marching bands or orchestras.
And you also don’t want a class that’s all computer science majors or zero philosophy majors. I imagine they consider other factors as well. The admissions staff may be liberal, but I’m guessing at most schools they deliberately admit some outspoken conservatives.