I started with a powerfeed spyder years ago, and learned to sight down the left side of the gun/barrel. As a right handed shooter, this "made sense" to me, and I went with it. Due to the range of paintball I found that over time, muscle memory counted more than any sighting (wood or speed). When I had a sterling this was definitely true for me.
I like center feed because the balance works. My phantom with vl200 offset to the right just felt weird, compared to the centerfeed setup I also got. The right feed on the sterling felt ok because the base gun is a lot heavier.
Which leads me to a another possible reason you see center feed. Manufacturing cost. AGD & CCI were the only companies that I remember built left/right options for their guns. Producing and stocking left/right bodies has a cost that many small companies may not have wanted to bother with.