C4 isn't user-programmable, a lot more expensive, limited dealer network. Small dealers can't sell C4 because they won't buy enough to make C4/ADI happy. Some consumers want to program their own without waiting for a dealer to get around to it.
AFAIK, Halo requires the C4 base and more setup than many customers can handle or are willing to do- great for dealers, but the number of Harmony remotes out there really ate into URC's market, evenn though they require dealer setup, too. Harmony's database was far better than URC's and the tech support staff were able to do things URC never would. The latert Harmony remotes also used IP control, when applicable.
BTW- did you see this?