In a word--money. Wood frame stud construction has been the norm in the US for mass housing for a long time, and I am given to understand that newer houses in the UK are being built this way. It is much cheaper than the heavy timber and 'stone built' constructions which have been the standard construction techniques in Europe for centuries. Stud wall construction can be constructed by carpenters of varying skill levels, whereas traditional European techniques require the abilities of skilled craftsmen.
From what I hear most people of modest means in Europe do not 'own' a fully-detached house or even a semi-detached one (in the US one half of a duplex). Home ownership is seemingly more important in the US and to achieve this cheaper construction was called for.
Roof construction is either 'stick-built' or trusses or a combination. Trusses are even more parsimonious with material than stick-built, but can be even more creaky than stick-built.
Edit Roof construction is 'stick built' or trusses or a combination.
On my bike ride today I looked at a house under construction in a neighborhood we could have bought in 39 years ago. There was a rail track right behind the house we looked at with freight trains going through at all hours; we passed. This was a tract development of light duty single story houses <2500 sq ft on 16,000 sq ft lots. Ten years after we looked, the rail line was taken out and it is now slated for a bike path.
The original houses (~ $65k in 1978) are now going for $500k to $600k for the lots. The new houses are two-story >6000 sq ft well designed and constructed. The permit on the house I looked today stated value of the construction $554k for 6400 sq ft. The outside studs were 2x6 and the walls were fully sheathed in OSB. High ceilings and a tremendous amount of 2 x lumber. Roof stick built with ridge beam and collar ties every other rafter. Demonstration panel indicates cladding will be a mixture of brick and stainless steel (scratches show shiny metal) panels with a grey finish. Roof will be standing-seam metal. There is a lot of quality construction in the US today.
In looking at this 6400 sq ft house yesterday I saw a lot of joist hangers, but I did not see what are sometimes called 'hurricane ties' (metal strapping tying roof rafters to wall studs. I am sure this is not required by our local code, but it would seem to be a sensible enhancement to a stud wall structure.
Twelve years ago I talked to guy who was having a new house constructed in a 'boom town' suburb north of Dallas proper. He wanted his builder to add Simpson Strong Tie connectors, but the builder resisted saying it would greatly increase the cost, complicate construction, was not in the contract . . . The owner persisted and himself purchased all the connectors he wanted. The builder grumbled but installed them, and in the end the builder said it wasn't that much extra work.