In the UK you struggle to get a mortgage on a wooden construction so have to be cash rich, you'd also struggle to get conventional housing insurance cover.
Nope thats not it. Many houses built in the UK now have a timber structure with a (mostly) non load bearing brick or blockwork skin on the outside. Most people wouldn't be able to tell the difference between a new build house that is timber or masonry structure, once it has been sheeted out inside. Timber cladding externally is less common.
I believe exterior timber was banned in London after the fire of 1666, and in many other towns not so long after that. A brick skin just gives you much more time to stop a fire from spreading. Even when the exterior walls are load-bearing brick, a lot of internal structure may still be in wood.
That's not strictly true, the rules [0] on what fire tests a cladding material must conform to are quite complicated and depend on how close adjoining buildings are and whether there are any windows in them.
Right, I'm sure the modern rules are very detailed. But at some rough level of walking around & looking at buildings, there's a step change right after the great fire.