Actually, I pick hymns for one primary reason: they are exclusively in a range that is easy to sing on Sunday morning - low! No temptation to play high notes. The secondary reasons are the suitability to adapt articulation to and the true poetic intent. The third reason is the logical harmonies that give us cues about clear intelligent musical form. Fourth is the potential for performance. A congregation is a very thankful audience - once the player is established, a 5 minute improvisation gets an uplifting response! Finally, the cost of music is marginal compared to the results!