Why are salaries so low in other parts of Europe?

Hi, I am from Northern Ireland (UK), and have always felt that our salaries in the UK are pretty poor compared to the likes of the US.

I think our median is something like £37,000.

However, this morning I was looking at average median salaries by country, in Europe and there’s a pretty stark divide with a lot of variability.

With the UK being ranked 14th in Europe, there’s countries such as Switzerland and Denmark having a much higher median salary.

What strikes me as worrying is the fact that countries like Portugal and the Czech Republic have median salaries as low as around €25,000.

These are supposed to be first world countries. Can someone please explain why their salaries are on average quite poo?