Homes started to punctuate the Hollywood hills after the "Hollywoodland" development kickstarted things (but largely failed, at least initially) in 1924. Description from pinterest.com. I searched for this on bing.com/images
When the cost of wood fell during the late 1800s, the shotgun house did indeed become the best way the poor could keep a roof over their heads. But, by then, shotgun houses had added a new element to the American architectural vocabulary. You see, shotgun houses gave us the Southern porch. We didn't previously have porches like that in America. Like the shotgun house itself, Southern porches are now all over America.