I had the impression that liberal arts students were highly profitable for universities, because they had no expensive labs.

It depends highly on logistics like class size. Many programs brag about small class sizes, which are great for students but anathema to university bean counters. These programs often try to subsidize the small program specific courses with huge gen ed courses, making the whole student body effectively subsidize these underperforming programs. Real nasty fights occur over which courses to include in the gen ed program because every department wants a piece of that pie to prop up their poor numbers. And this dynamic is definitely much worse in humanities.

Edit: also instructor composition, meaning the proportion of instructors in a program who are senior/tenured vs new vs adjuncts. Class size and instructor salary are nearly the whole equation.