£50k isn't a huge amount. As has been said, when you compare the net income with that of someone on a low wage that is topped up with tax credits, the real gap isn't that big.
Many in the £50k range will have more non-luxury outgoings For example, they'll have to spend more on clothing such as shoes, suits, dry cleaning.
Are there any minimum wage jobs that require you to turn up in a suit? Lower wage jobs that I did, I could turn up in casual clothes, or was given a washable uniform.
I think people tend to take their own situation, imagine what it would be like to have an extra £5k-£10k coming in each year, think how well off they'd be and what they could do with the 'extra' money. But that isn't the reality. Moving up a couple of income levels has other implications.