The current zeitgeist emphasizes increasing the number of students pursuing STEM. Many hypothesize that classroom instruction is one of the reasons there are disproportionately high failure rates in STEM when compared to other fields of study. While there's always room to improve course instruction, STEM courses are different from social science and humanities courses because they tend to be cumulative.
For example, a proof-based course will build up a series of results. So, a lack of understanding early on will compound as the course progresses. On the other hand, in non-STEM courses, units of study tend to be more independent.
So, presuming a student understands ~80% of each unit in a STEM class with 2 units, that student may only understand ~64% of the total material, while in a non-STEM class that student may understand ~80% of the total material.