Mike...
Because...
1. I, too, have pretty much standardized on a 5/8" diameter for my kitless pens.
2. I, too, make my sections longer than what you normally find in a kit pen (I certainly don't have the biggest hands out there, but the kit sections are way too small for my tastes).
3. I, too, think a pen with a cap and body of the same diameter is very sleek - most of my kitless pens are made the same way.
4. I don't find the occasional translucent pen, where you can see the innards, all that bad - actually I find most of them pretty slick, and they are often only really completely see-through in bright light...like when being photographed....
5. I think the photo is probably giving everyone a distorted sense of the actual proportions of the pen. In person, a 5/8" diameter body is not all that big, and the section - in order to fit inside the 7/16" hole - CAN'T be that big.
...I think this is a GREAT looking pen!
Sometimes, though - depending upon the material and it's pattern - making a pen with the same diameter cap and body results in a finished product where it is tough to distinguish where the cap and/or body begins or ends. One poster mentioned adding a centerband (although I think it was in the context of providing strength to a thin-walled cap) - since we haven't seen the cap yet (so you may have already thought of this) a "centerband" consisting of a segmented contrasting material can also serve as a subtle (or blatant, depending upon the contrast) visual cue.