That in no way absolves them of the responsibility to treat you like a human and give you a simple "no thanks."

This attitude it toxic and feels like you're looking to turn an interview into a lose-lose situation. It doesn't have to be.

I feel like people have forgotten the golden rule... everything has become transactional.

Even if it is transactional it still makes sense. People talk and if a company gets a bad reputation it will be harder for them to recruit and retain which translates into a cash cost.

likely far more than 6 hours, probably more like 50+ with all the people and tasks involved. But they also cost this as part of their model - I don't think it's fair for individuals to eat the cost of the hiring process dictated by prospective employers; that's why in-demand candidates won't put up with their nonsense.

Sure, but they moved on, have stopped wasting their time and missing opportunities.

You, on the other hand, are quite possibly still thinking about it every day, and turning down or delaying (and missing) other offers.