People of today tend to think that a tune and set of words are one. For example, if someone put dirty to words to "Silent Night," he would probably be stoned.

In the past, tunes and words were much less connected in people's minds. For example, scholars have found at least 88 sets of words to the Greensleeves tune, ranging from reverent to nasty.

I suspect that in the 1700's and 1800's, when new denominations were starting and their humble organists did not have much learning, it was far easier to put a poem to a tune that everybody already knew.

The question "why should the church steal all the tunes?" really means "why should people play what they know already?"

If it burns you up, Mo, do what I have done. Study the tune, play it for a while, and see what it takes to make it sound traditional. It's fun to do.