not worth the investment, and as already mentioned, they like to work with people, not cut them out of the market when they are there to help. It's just easier for them. Less resources, less headaches, less tech support when things go wrong. Plus it makes them look real nice, by not pushing other's out of the market.
Honestly, they made that chipset because no one at the time could make a decent one. Plus it was their MP version that they made available to support desktop CPU's so it wasn't a big deal. It quickly lagged behind in features though, and they probably saw how it wasn't financially sound to make chipsets.