Cosmodragoon,
Pure speculation on my part:
1. Perhaps saves width to maximize concealment?
2. Ditto for an ounce or two?
3. It most probably just allows Charter to use much of the same tooling and internal parts it uses for the .22's or .38's, thereby keeping down cost. I suspect that changing the geometry of the cylinder from 5 (72 degrees each trigger pull) to 6 shots (60 degrees each) would change almost every operating part's machining and fitting angles & tolerances.
Just guesses--maybe it will help smoke out the real reason(s).
Why not contact Charter and ask? While you're at it, see what they say about bobbing the hammer or replacing it with one of their purpose-built bobbed hammers. Can't hurt to ask.