I’ve played in music ministries for 35 years.
The main answer is simple -
most people can’t sing…
I’m half-joking, though. It’s not really that people can’t sing, but the hymnals are written to be as simple as possible to be as inclusive as possible.
On a more serious note, when I am in church, and I hear someone who cannot sing singing, I dont mind at all. Everyone loves a good show, but the devil came through the choir. We’re not in church to show off. Hymns are prayers. And, if someone cannot sing - but is making a sincere effort - I say, all the more power to them. Let them make a joyful noise unto the Lord or to sing a song of lament. So, too, if a hymnal is of modest quality, it helps facilitate the audience by accommodating the one singing - or, what is the same, praying.
Another (less well-known) reason for the structure of hymns was the architecture of old churches, cathedrals and monasteries. The drone sounds and loose rhythms of older pieces was less rigorously defined as something like a Mozartean concerto, so the very drone notes could reverberate throughout the church. More intricate pieces are usually best played in a salon or a chamber where there is less reverberation, so you can hear the intended effect better. This was usually a deliberate choice and collaborative effort between both musicians and architects (so important was the matter to them back then); and, in fact, we still have this “collaboration” between musician and architect today, even in secular venues, such as when a heavy metal guitarist might have trouble with playing fast solos in an large arena, or a hall where different social events echoes so much you can’t tell what a speaker is saying because diction and clarity tends to get lost in reverberation.
That is not to say there are not more elegant works. Not by far. But, if you wish to hear elegant sacred music, you kind of have to pursue it yourself. I love to listen to old masses and sacred pieces by Mozart, Bach, Beethoven, Faure, Gorecki and on and on… They are a side to Catholicism which few people know and understand, which is very sad because Catholicism sometimes gets a “rep” by the general public for being a dirge… The granduer, joy and exaltation the works of the old Masters brings elevates one’s conscience to the Glory of God all loves excelling by many of today’s perceptions.
Blessings,
Wm