Another factor is that people are living separately from their extended families and change what type of building they live in at different points in their lives, for example:

• Single adult - rented flat or small house.
• Couple - rented larger flat, bought small house.
• Couple with kids - trying not to rent, buying larger house
• Couple with adult children - no longer need the space, buy smaller house

People also like to have gardens and pets, which is easier in a house than a flat. Ownership is also a factor, owning a flat doesn't make much sense when you have to pay ground rent and a mortgage.