Sales, I would imagine. I'm carrying a clip point model at the moment, and I own every plain edge model, and the serrated Vaquero. The half serrated models don't do anything for me. They're a most inoffensive size while still being a decent cutting knife. I might have to buy another clip point before they're all gone, although if they haven't been selling well they may hang around for a while anyway.
I'd say their weakness is that the handle shape is slightly awkward for larger hands (like mine) as it's just scaled down from the larger models. I think the optimum for my hand size is the 4" version but that is less non-knife-people friendly. Someone commented that on the previous version Voyager the smaller models were the most comfortable, while on the newer model it's the larger models that are the most comfortable.