The UK has a high population density, and a lot of land is still owned by old nobility who don't really care to sell it.
In the rest of Europe prices are much lower, I'm currently building a house in Northern Europe on the outskirts of the capital (within city limits) and we paid €30/m2 for the land in 2019.
I'm curious about US price of land. I looked into building a place in the UK, and the price of land alone was a blocker.