Summary: The mainstream ear has changed. As a result, traditional choral compositions have become less accessible to mainstream audiences, but the form of choral music remains accessible. People who participate in choral music train themselves into a traditional taste as a side-effect of participation.

Sung pentatonic music seems to be accessible to everyone from a young age.

For most things beyond that, our brains need exposure to the form to be able to appreciate it. This affects rhythm, melody and instruments.

My three-year-old hates the sound of guitar distortion. I am confident he will acclimatise to it.

Accessibility of traditional choral music will be influenced by what the audience knows. People who grew up with sung carols on at Christmas will be more open to it than people who have grown up with post-war pop Christmas.

Everyone now living in the developed world has been exposed to beat-backed major/minor easy-listening music by television, films, car radio and shopping centres. This is recent. People a hundred years ago did not have the same ear. The large choral work Elijah was easy-listening to audiences who had heard sung mass hundreds of times.

In 2025, a church music director wanting a twentieth century composer would schedule Rutter easily - Rutter writes music that suits the ear of pop Christmas. They would prefer Howells if they thought the congregation had a more traditional ear. They would schedule Messiaen only for a particular occasion.

The OP wrote - "It has struck me that most recommenders and lovers of choral music [are] themselves singers (or conductors) of choral music."

It is easy to get involved, so many people who are curious get involved. Once involved, people will find their tastes becoming traditional as a side-effect of exposure to the repertoire. This creates a running division between people who participate and the mainstream.

Note that before seventy years ago, almost everyone who loved music would have participated in it, even if only singing to young children or helping out at church. Outside royal circles, the practice of loving music yet being a pure consumer is a recent phenomenon.

Some forms of choral music will have a different relationship with pop than high-church music. For example - Gospel, accompaniment to rock songs like /Under the Bridge/ or /You can't always get what you want/. The Beatles were a mainstay of post-war pop, but /Because/ on Abbey Road has the character of a Renaissance choral work - George Martin was classically trained.

The mainstream ear may be making another shift now to more sophisticated beats with closer melodies (smaller pitch jumps) and simpler chords. If it happens, we will see evidence of it in popular Christmas music. As far as I know there has not been a new addition to that repertoire since /All I want for Christmas is You/ which is c20 pop.