A sneakier thing that some of my professors did was to inflate the lower percentile of grades. So not everyone would get an A, but nobody would get lower than a B-/C+.
Of course, sometimes 50% of a class fails because the teaching is shoddy, or the grading is unfair, or the prerequisites weren't properly set or enforced. It isn't always a failure on the part of the students. Failing grades are inherently a failure of the system to prepare and guide a student through material. A common symptom of that systemic failure? Lazy, unmotivated students.