There is, actually, a not insignificant repertoire of secular choral music although it’s lost a lot of its popularity. The liner notes for one collection of Aaron Copland’s music made a comment about how it was strange that Copland had written very little choral music given its indigenous popularity in the US in the first half of the twentieth century.

But yes, solo vocalists have been the primary mode of vocal music in English-speaking culture which presented a challenge in creating post-Vatican II liturgical music which was intended to echo the local culture (something that Dennis Day noted in his book, Why Catholics Can’t Sing). Folk and rock both tend not to work well as a format for congregational music although the former works better in my opinion. Certainly, I don’t buy Day’s argument that the obvious liturgical choice is old-school hymnody (I lean more towards incorporating more of Black gospel instead).

I wouldn’t call the various harmony-based groups like Backstreet Boys or K-Pop as choral music. What makes choral music choral is the fact that there are multiple voices singing each part in the piece.

No I wouldn't class the artists as choral artists at all, I'm just pointing out that there are examples of polyphonic singing with multiple voices in pop music, it's just that it's usually accompanied with a rhythm section. Pieces that feature choral singing can be very accessible, although acapella music usually isn't. But take the example of Pentatonix someone mentioned earlier (which isn't really choral singing either because of the lack of voice doubling). What makes them accessible is that they use beat-boxing to provide the rhythm line for the punters.

What about groups like the aforementioned Pentatonix and The Harvard Opportunes. They are quite literally multiple voices singing each part in the piece.