I can understand people wanting a warmer and sunnier environment (unless you have skin cancer). I do find around 23 degrees is my preferred day temperature and about 12 degrees at night. In the Summer the Mediterrean is often too hot for me with 30 plus degrees and 22 degrees plus at night etc. I would definitely avoid the Tropics and the Middle East based on temperature. I like my garden and in hot countries without high humidity many plants die look at say Malta a few cork trees and prickly pears. Having said that I only spend a few hours a day outside as probably a lot of people do. Lying on a sunbed or swimming in a pool I find very boring after 10 minutes. I like the look of NW Spain - its got wooded valleys and hills, not scorched in the Summer, but a pleasant 23 and 13 degrees in the winter.
Its nice to visit other countries but living there is different to me, some Brits retire to other countries, but find themselves a bit isolated especially if they don't become fluent in the local language and culture and customs. Nearly half the Brits that went to Australia on subsidised passages came back, sunnier days was not enough to keep them there, they missed something.
Having Italian relatives I know the Italian NHS is not as free at the UK NHS is or as comprehensive look at all the specialist hospitals in London. Doctors come from all over the world work in the NHS in great numbers. Nor are social services as free and extensive as in the UK.
I like the UK because it had 4 seasons, there is such a variety of places to visit in a close range, great heritage, think of all the theatres, sporting venues, music venue/festivals, galleries and museums, National Parks, film and literary festivals. It all depends on what people are interested in. Sorry, but places like Dunedin, Northern Sweden, Canaries, Holland etc can't compete for me. The UK has a 65 million diversified and in world terms affluent population that creates demand for a large range of leisure services. In contrast New Zealand's population is 4.8m and very spread out.
Ref corruption - obviously none of those posters really know other countries very well or watches the news about other countries, look at Lebanon recently or living in countries with dictatorships like Russia/Hungary/Belorussia or Mafia in parts of Italy.
Ref Not being in the EU - neither is most of the World or a lot of the countries mentioned as destinations to live!
Ref: Pensions - most private and occupational pensions can be paid anywhere, but you will likely pay tax in your country of residence to live there as your main home. If you are no longer in the UK you may give up residence or have to pay tax in 2 countries i.e. UK plus one other. UK state pension is frozen if resident outside so does not go up with inflation. If in the EU it went up with inflation. but this may change from 2021. Sometimes the UK does a reciprocal deal with a specific country to allow it.