Some Oxford Street stores do make lots of money but there are many others where ten minutes in the store is enough for you to see what is going on. The whole range can be on show whereas in your regional town there is a fraction of the range. But you can experience the brand.
Adjacent to Oxford Street is Tottenham Court Road. This was legendary in the 1990s for computer shops with fairs in nearby halls where you could buy components for competitive prices, as if nobody was paying VAT. That scene went a long time ago for more flagship stores to come along. These flagship stores don't have to make sales to cover the rent. Microsoft are part of the theme park.