Those on higher salaries also tend to be those with the skills (and experience) sought by other countries. It does make them much more mobile.
In research published in 2023, The UK came out as the 7th most expensive place to live in Europe. Due to globalization, corporate jobs in Europe increasingly use English as their working language, which makes it even easier than before for Brits to secure well-paid jobs abroad, even if they don’t arrive with the local language. Locals, who do not speak English, now loose out on these kind of jobs to foreigners with fluent English.
The Belgians, for example, live so much better than the average Brit. Their housing is affordable; their food is some of the cheapest and best in Europe; very, very cheap, state subsidized child care and their education system is also stunningly good. The average Belgian teenager speaks at least three languages (Flemish (i.e. Dutch), French and English.
Switzerland, whilst more expensive than the UK, does have some of the highest salaries in Europe. On average you would live more comfortably than in the UK. If you chose to work in Switzerland but live just over the border in France or Germany, you really can live the high life and on only one salary if you so choose.
In the UK, Private school fees are often a consideration for higher earners (and school fees have risen much higher than inflation. An expat job abroad might well include the cost of private school fees (if you wanted your children to be taught in English). In many European countries, however, private schooling (in the local language) is not at all common and where it does exist it is often a fraction of the cost of the UK (about €1,000 per child, per year - as they tend to be run on a not for profit basis). With the local schooling option, (private or not) your child ends up fluent in at least one other language.