Why Do We Lift Up Our Hands When We Sing?

I've been noticing this phenomenon in worship services: Some people will lift up their hands up when they sing. Interestingly, they only do this when they sing contemporary songs. More interestingly, usually they only lift up their hands during the refrain. Most people, if not all, will never lift up their hands when they sing "old songs," known as "hymns."

Perhaps we shall stop and ponder. Why do we lift up our hands when we sing? I have been pondering on this question as I also sometimes do lift up my hands when I sing, and I do sometimes lift up my hands when I sing "hymns" privately in my own room. I wonder if I am actually satisfying my own desire, rather than satisfying God's when I do that. Why so? Because usually I lift up my hands when I "feel" like lifting up my hands. When I don't "feel" like doing so, I won't do it. So, at the end it seems that my singing is all about me, myself, and I; and not about God. I wonder...