I don’t know if this applies to college, but for high school teaching, the standard expectation is that it takes about a 1:1 amount of time of preparation/grading/student-help/etc. to classroom face time (more if you’re new or teaching a new-to-you course or a course with a large lab component with setup/takedown).
Nearly every teacher I know takes a ton of work home (and no we don’t get paid for summers “off”) and cannot get all the grading/etc. done within the school day. At my school, the school day itself is over eight hours including helping after/before school. But I know that we are a bit on the high side for a public school.
So at a highly-ranked high school, it might be expected for a full-time load to be teaching four courses. Plus usually other supervisory/advisory/activity obligations.
If a college professor is teaching half as much (but maybe has TAs?) - then my guess is that this professor is 50% teaching and 50% research. As I understand it, the research typically leads to a lot of funding, prestige, and accomplishments for the university so it becomes a large priority for faculty.
If someone wanted to add two more hours of work to my day every day for the same pay (or even for more pay) - I would certainly balk at that, because like everyone, I have other obligations in my life. Going from 8-10 hours/day to 10-12 hours/day of labor with no consideration/compensation is certainly not something that should be expected even from giving, helpful, “we’re in this together” professionals.
The “we’re all in this together” I would apply to the fact that for instance, my colleagues and I have volunteered to do summer book collections, committee work around how to improve sanitation in schools for the fall, and other helping projects for our schools in our own free time.