Makes me wonder who, other than hobbyists, were listening to all of these shortwave stations. Diplomats? Students? Would-be revolutionaries? Even the religious broadcasters.
In much of the world, radio stations were located only in the big cities. In rural areas, listening to local "tropical band" SW stations was very common, and there were many, many stations. All over Africa, the Middle East, Asia and Latin America there were many, many SW stations. They were listened to both locally and in rural areas where there was often no telephone service and of course no radio station.
International shortwave began in earnest in the 30's and was a popular way to hear entertainment and news from other parts of the world. It was extensively used in WW II for propaganda by both sides of the conflict. And then, the Cold War caused many countries to broadcast their preferred ideology. Other nations promoted their culture and tourism via shortwave.
In most of the world, radios had SW and AM. When FM started growing in the late 60's outside the US, more and more people wanted FM radios and manufacturers traded FM for SW on their products, so SW began a slow fade over the next 30 years.
As an example, in the late 60's, Quito, Ecuador had over 30 AM radio stations... all fulltime and full signal. Yet there was one SW station from a city about 100 miles or so away that consistently showed up in the Quito ratings... not very high up, but it was there. That SW station (it had an AM, but it was separate only for its home town) was one of the highest billing stations in the nation, despite being in a city that was not even in the top 20 in population.