And as for the difference between HASS and STEMM contact hours: a lot of STEMM contact hours are labs, where students work on specifc exercises & activities, supervised by lab techs and often postgrad teaching assistants. Supervised, not intently taught in that the students are doing the work, overseen by staff (and not always lecturing staff).
This is entirely appropriate to what the students need to learn.
In the Humanities, often what students need to learn is through a lot of reading. Now, I could gather all my students together in a "lab" for 8 hours of reading, supervised or overseen by me. We could all gather physically in a big room, and read. (It would have the advantage that I would know that they'd at least read the set material). Actually for most of my modules, they'd need to read for nearer to 2 full days.
So we could do that, and that would be contact hours.
But it would be ridiculous.
See why you can't compare different disciplines, which require different modes of learning? There are some types of learning/teaching in common as well, of course.