Why can’t they just do the right thing from the get-go?

Because like all nice things, people abuse them. Not to indicate that Carnival Cruise is some saint here, but the reason most companies don't just default to "benefit of the doubt" is because there are a ton of very bad people out there that abuse any inch a company will give them.

My step mother was one of those entitled ass people who thought the world owed her. One day she put on some act about a late fee and the person on the other side of the desk was saying "oh I'm sure there's something we can swing…" And having enough of her shit, I was basically, "Do not give this lady a wavier on that late fee, everything she just said is some massive warping of the actual truth!"

Maybe it's because of her, but I find it difficult to ding companies who don't default to "benefit of the doubt". I'm glad the lady got it sorted out. But shoot, I've got massive distrust of folks in general and my step-mother is a lot of the blame for that. Side note, that's likely unhealthy kind of stuff that I should one day sort out.