Very few people are really rich. OK , it's all relative,if you're living on the streets, someone with £50 is rich to you, and if you have £1m, Bill Gates probably won't think you're rich either. The government and Uk media, seems to think rich begins at about £40k a year , when they take a much bigger chunk of your wages, but you can't buy a house in SE England with that income. The top 1% of earners begins at about £80k but encompasses sports and pop stars earning mayve £20m+, and there's a massive difference in your lifestyle there.
So it's more a case of why are some people poor and some relatively well off. In 99% of cases I would say it's a combination of intelligence and hard work.