Nice to see a response from CX, thanks for that.
I would imagine that the savings are not that small, and that the global recession, rise in fuel and insurance costs and downturn in business travel, coupled with the need to conserve cash would be perfectly reasonable justifications for Cathay to keep its airside facility shut until 8am.
After all, it is not as if no Arrivals facilities on offer.
The T3 AArrivals lounge is actually not that bad, to my great personal surprise. I last used it two weeks ago, and was impressed. It is great improvement on the previous AA facility (scroll to end of page):
There are plenty of shower suites, 29 in total, and they are spacious and well ventilated.
The AAngel on the desk was helpful, if overly chatty.
And they do indeed offer hot bacon rolls. Not as good as those offered in the BA Arrivals lounge, but bacon rolls nonetheless.
T5 has excellent arrivals facilities which are open from 0530. Perhaps you should try another airline next time you fly into London from HKG 😉