Why was radio so popular in the Pacific Time Zone?

I came across this surprising diagram (left) on page 105 of Warren Dygert's 1939 book, Radio as an Advertising Medium (McGraw-Hill Book Company, Inc.: New York and London). For a better view, click on the image to enlarge.

The chart shows that in the Pacific Time Zone, a whopping 95% of all households (here described as "radio families") owned at least one radio (probably in 1938).

This high percentage beats the Mountain Time Zone and the upper Midwest by 15 points; beats some parts of the south by 35 points; and even beats the urban Northeast by 3 points. I've never seen these data before, and find it very interesting.

Of course, in total number, the Pacific Time Zone had just 2.5 million "radio families," while the Eastern Time Zone had more than five times as many or 13.5 million.

The reader will forgive ISLR's obsession with the West Coast, but what, if anything, explains why radio ownership was so high in the Pacific Time Zone?

Good question, and one that I'm not yet prepared to answer definitively, though I do have my theories.

Chief among these is the relative prosperity of the Pacific Coast throughout the Great Depression (compared to the Midwest or the South, for example), combined with a fair amount of rural, sparsely-populated territory spread relatively evenly between big cities such as Seattle, Spokane, Portland (Oregon), San Francisco and Los Angeles.

Prosperity meant the ability to buy a radio, which residents in many rural, more depressed parts of the country didn't have. Rural entertainment choices (lack of movies, lack of neighbors) gave radio appeal as a household necessity in the wide open West. Proximity to big cities (and network affiliates with powerful transmitters) made radio a practical choice, with nationally-produced entertainment and news programs readily available via consistently good radio signals.

Anybody else have any theories? Geography? Terrain? I'd love to hear any and all ideas.