I do, too, but polyphony is a cutting-edge innovation, on the time scale of Christian liturgical music - it only showed up in the 14th Century or so! Just as some congregations don’t allow instrumental accompaniment, some think that everyone’s singing the same melody is a key point of worshipping in song. I can see the reasoning, without agreeing that it’s of importance.
It’s a too-tidy sort of reasoning, imho. Set up by those who like things tidy and under their control. I am glad the Germans are still taught it.