I think it's a lot about economics, too. Choirs of any significant size have to be amateur. It's hard enough to do a 4 person band playing popular music full-time, with 20-30 people performing more niche music it just doesn't happen.

Small group a capella is slightly more viable, but it's very "amateur coded": even very good a capella groups perform a lot of covers, and rarely stick with one genre. They perform whatever they want, which is often also things with commercial appeal, but isn't ideal for long-term musical identity building.

Take Rajaton for instance. Extremely technically brilliant, but their own compositions are a relatively small part of their repertoire (and still more than most a capella groups!). Pop music covers and Christmas music are obviously a big part of what makes them commercially viable, in addition they perform commissioned work from acknowledged choral composers (Mia Marakoff, Michael McGlynn). When they do the occasional album with good stylistic coherence and their own compositions (like 2016 Salaisuus) it doesn't look like a commerical success.

>I think it's a lot about economics, too. Choirs of any significant size have to be amateur. It's hard enough to do a 4 person band playing popular music full-time, with 20-30 people performing more niche music it just doesn't happen.

That really depends where you live. In Vienna you definitely get all-professional choirs of that size for instance.