Yes there was big band and jazz but that was mostly in the cities. Crooners fronted the big bands and were good for movies. Everyone else with any natural musical calling (mostly self taught) played country. The Grand Ole Opry was a staple of life up and down the Mississippi and all points east and west. If you played guitar, you played country. There was no rock n roll yet.
The truth is pop aesthetics have been a part of country music since the beginning. Country without any pop elements is called folk music and, save for one or two bubbles which expanded for a few years and then popped, nearly nobody in the second half of the 20th century listened to or cared about folk music. Comparatively, country music in the same period was a hugely popular genre and lucrative industry because the truth is, its always been both informed by and informing mainstream society and culture. Finding ways to connect these things people dont know about country music to the things they do know about everything else is half the battle. Once those things start clicking into place it unlocks all kinds of doors.