There's a line of research that shows that high quality one-on-one instruction gets you up to 2stdev gains in learning performance.

If you can afford to increase the professor to student ratio and make them available for office hours, you probably do see increases in performance. Is it due to better motivation? Seeing an academic up close? Actually better explanations you get from an expert in the subject? Hard to say.

But I also mentioned that there are often thousands of students all trying to take one course. And the schools simply don't have the space to fit all of them in one session since I believe the rules are basically that it needs to be held in a lecture hall big enough to fit every enrolled student, and teachers don't have the time to teach 4 different sessions by themselves on top of their other duties. Maybe class sizes are just smaller elsewhere, but where I went to school it was not unheard of to have multiple thousands of students needing to take one class that was required for practically every STEM major in a given semester.

So schools offer multiple sections of the same class to share the workload. E.g. in recent years Computer Science 101 - often the most popular class on campus.