> "for some reason the number in USD is equal to the number in GBP for almost everything, even when GBP is 1.6-2.2x the USD"

Price is set by willingness to pay. full stop. Cost for goods is almost always worked to, backwards, from price targets. Exchange rates don't enter into it, except as pertains to costs.

GBP prices remain 'close' to numeric USD, because people still buy products at those prices. Looking into why they do, leads to interesting questions and analysis about disposable income, taxes, psychology, etc - but it's largely irrelevant.

It is that way because it works.