I think there is a huge "grass is greener" issue going on.
Firstly, if you have a huge amount of money and can afford not to work, or have a business that you can run from anywhere, then sure there are probably better places to live that have cheaper housing and less pollution.
However, if your career means you need to work in a major global financial centre, and you earn over the income threshold that makes you better off in HK, I really don't think there's a better place to be. Which other global financial centre would allow you to; pay very low tax and therefore save and invest a lot (assuming you're sensible and don't overpay on rent); live 10-30 mins from your office, and yet also be able to be outside hiking up a mountain, visiting great beaches or on the sea in under an hour; employ domestic help that allows you to spend your weekends enjoying quality time with your family, not cleaning washing shopping; enjoy great public services including an almost free healthcare system and very cheap and efficient public transport; take taxis everywhere because they're so cheap; dine out in a fantastic restaurant at all price points every day of the year; earn enough to be able to travel and enjoy seeing the world? My list could go on.
Sure, if you want to downsize your career you may be able to go and live somewhere with cheaper housing, no pollution, plenty of outdoor activities - but for most of us with careers in HK that kind of location is not a viable option unless we want to give up a lot. The options would be say London, New York or Singapore, all of which have compromises.
I know a lot of people moving to London; taxes are high; unless you live in central London which is as expensive as HK, you will have an awful commute on a packed hot public transport system; your family life will suffer as domestic help is very far from affordable; taxis are expensive; if you like the great outdoors you're looking at 3-4 hours drive in Friday night traffic to get to anywhere properly rural or beachy. I love London, but you need to be significantly more wealthy to enjoy the same standard of living there than you do in HK.
Singapore is the other destination that people seem to list, and it does tick a lot of the same boxes as HK - but if you like the great outdoors you will be very bored in Singapore - that would be a major negative for me.
So for me, in the middle of a career I enjoy and just starting a family, HK ticks all the boxes. It's not perfect, sure. I'd love to be able to live in a property I owned here but that would only be an option if I downsized or liquidated a lot of other assets. I wish the pollution was not as bad. But when I hold HK up and compare it to other locations where I could continue my career, it wins by a mile.