Cost of supply of labour vs demand for labour. Sadly, it's a market.
Rant below!
This is why you get the same role in the same company, but with different pay across the globe (or within countries). Little has to do with the "cost of living" in those geographies, instead it is all about the cost of labour.
If you live in a place (e.g., silicon valley) with loads of companies looking for the same "talent" -and creating a shortage - then the cost of that "talent" goes up: Workers have more money to spend on housing, food etc. So those costs go up too, creating very high cost of living places, which then "justifies" the higher wages. However, if you look at inflation - as we have had recently, almost 30% over the past 3 years - you don't typically see wages rising in line with inflation. In fact, my company has reduced wages for new hires because there is an oversupply of "talent" right now due to so many lay-offs in my sector (Tech). Large companies also don't tend to increase wages with profits, instead that profit goes to the shareholders.
My easiest jobs were the most high paid and required advanced education (e.g. a PhD, which automatically reduced the labour pool). My hardest jobs were call centre, care work and waitressing pre-PhD, which were the lowest paid.
It also has nothing to do with "value" or inherently producing something of high "value". My company is involved in making products, which although generate large revenue, are almost useless to society. Additionally, people working for my company in "everyday" jobs (e.g. shop floor, warehouse etc.) still get paid minimum wage.
I think many people end up in lower paid jobs because when they were making decisions (e.g. about further study, where to live etc.) they either didn't know enough about jobs and the labour market, or had fewer opportunities. E.g. a 17 year old thinking: "I'm going to do an English Lit degree because I love the subject. Once I have a degree I will get a good job I love, purely by having a degree". The 17 year old's parents never went to uni and are on minimum wage so cannot advise. Mabe they live in a part of the country with few high quality jobs (e.g. a coastal town) and want to stay close to family, so when they finish school get a job as a cleaner or in a bar. State schools and universities are useless at career advice. This decision shapes the child's opportunities for life. It has nothing to do with lack of hard work, intelligence, an easy job etc.
In the past, if you worked full time you could afford basic things - almost like a right, you didn't have to count yourself lucky to have a car, a house, food, heating. The dad who left school with 0 qualifications and supported a family of 5 by working in a factory, even buying his own house. Nowadays, you have professionals (nurses, teachers) using food banks, freezing in the winter and being told to count yourself lucky because it could be worse - don't you dare expect a holiday or some new clothes.
Why should a full-time worker need universal credit? They shouldn't need it: A full time job should pay enough for food, rent, luxuries (e.g. the cinema, new clothes, a take away, a coffee out) etc. The Government has well and truely f*ed us. Instead, the Government has chosen to divert taxes to subsidise companies paying low wages - it only helps the company's profits, which isn't passed on to workers, nor is it reflected in their tax. Don't start me on private landlords and buy-to-let, with housing benefit (aka our taxes) directly benefitting landlords and the banks.