Can I ask why? Just personal preference or problems with them?

Also, are the Phil Wood bearings a good replacement? As far as I understand they are not strictly speaking the right type even though the dimensions are the same. Phils are 6901 vs. Surly New Hubs take the angular contact version 7901. 7901 is designed to bear axial loads as well as radial and I read it somewhere that 6901 would wear out faster in the "new hub" style system without the shouldered axle.