Maybe because we write differently than they did back in the day? When you write a buddy in an email or letter, how many times do you say their name? Even if you're complimenting them? I don't even say God or Jesus much when I'm praying directly too him. He knows I'm talking to him so why repeat his name a hundred times in a prayer (some people do do this and I find it quite odd... it just feels like they have to keep reminding themselves who they're talking too)? It's just different times. In the psalms, O Lord and such are interjected in places that we don't interject names or titles and stuff today. Forcing God's name into a song where in normal writing, we would never do it with anyone else, King, Queen, or otherwise just seems forced and out of place because we don't talk like that anymore. All the O Lord and stuff in Psalms remind me more of how they wrote back in Shakespeare's day.
And "You Raise Me Up" was never a "Christian" song. It was adopted by churches later but I never thought of it as Christian song. Seems to much of a love song... in a "I'm in love" kind of way. And forgive me but I feel uncomfortable singing songs to God that feel like you are "In love" with God rather than just "love" God. I'm not in love with my mom or my dad. That just sounds perverted and twisted. I do love my mom and dad though. Too many "Christian" songs that directly addressing God sound more like the person is in love with someone than just love God. If they didn't stick God's name in there, I would have thought they were singing to a boyfriend or a girlfriend... and to be honest, I'm disturbed they are singing to God in such a way.