They actually do not hide the main reason and state it first:
"If we start paying everyone the highest wage our compensation costs would increase greatly, we can hire fewer people, and we would get less results."
That's why I like their approach and communication. As a Ukrainian, I would be happy to work for CA salary here, but I do understand that a good local market rate is enough for me if the job is great.
EDIT: and one more thing to add here: as an employer, you usually prefer to hire people whose motivation is not only money. You want to work with people who like the job and their colleagues. The current market practice is to pay local rates. Thus any company that pays much more, has to address the challenge of filtering out people with "incorrect" motivation.