I assume it would be more probable that timber framers have banished L.A.

Most timber frame companies require large amounts of space, and that comes at a high price. I don't think that most timber frame companies can justify the cost as easily as other types of builders who require less space and push out higher volumes.

Since most timber frames are cut and fit off-site it may be more practical to just ship the frame ready to be assembled.

I am sure that some builders do use timber frame companies to supply them, but probably all they want is trimber anyways.

Another issue could be seismic activity and the requirements an engineer would place on a structure, maybe?