NPR has an interesting article?on the rise of the Glock pistol in the United States and?Paul Barrett’s book?Glock: The Rise of America’s Gun which presumably goes into more detail.
It basically boils down to “reliable, accurate, simple, durable, high capacity, and good timing”. I think if you look up the dictionary definition of those words, the dictionary will have a picture of the Glock pistol. It’s no surprise they’re popular — I’ve owned three over the years.