My point is that supply and demand is heavily affected by priorities, and so you need to account for people's priorities if you want to make assumptions about what the difference in size means.
There is plenty of affordable land in Europe, but instead we're seeing even people who do not need to move to more expensive cities for work still do so because we willingly choose smaller houses.
That is not to say that there aren't plenty of people who would like more space, but I've personally worked with people who "wanted" more space, but only if they didn't have to move even one fare zone on public transport further out, because they liked to be dead centre of a major metropolis.
My example of a French castle was not random - I'm considering retiring to France eventually, and for the cost of my house in London, I can literally buy a castle 10x the size of my house, on huge grounds.
Yet today I would not swap my house for a castle even though I work 100% remote and could do so if it suited my lifestyle, because my location currently matters more to me than more space.