Price/income increases don't happen in a vacuum, it takes a while for it to become normal. If you got a £50 bonus and decide to get yourself to a McDonalds, only to find they've raised the price of their burgers to £50, would you still buy the burger? Your situation would be the same as before so logically you would, but of course you wouldn't. That price increase has overall lost Mcdonalds money, since now you're not buying anything (assuming everything else they sell also went up a proportional amount).

Obviously there are essentials that can effectively be at any price and you have to pay them if you can afford them, but everything else is fair game.