American and British degrees have more utility. They are more internationally recognized and in circles that value degrees from certain schools, they value American and British degrees. Easier for such degree holders to get higher paying jobs out of undergrad, although also more volatile as the costs are high and not everyone gets those high paying jobs so economically the degree can be highly costly for the parents.
That said, I think that the cost aspect of the degree isn't as important of a factor given that raising children in HK is already expensive so undergrad degrees might not make up the bulk of child care expenses. In HK I've met many graduates of Southern California, a school I'd never heard of until I moved to HK. Even after working for 10 years, none have earned back the cost of their degrees and I doubt their parents care.
So when they do the cost benefit analysis, there's more value put on the potential benefits of the degree vs the cost. So I think it makes sense that American and British degrees are favored - they've got the highest potential economic upside.
On the flip side, my cousin bought an apartment in Vancouver for his daughter so that when she's eligible for high school he'll ship her over to Canada (with her mom). We have a large family and he's hoping my cousins will toughen her up. I doubt many parents have a similar mindset. He doesn't think she'll be economically successful regardless of what school she attends.