Because they can, and they know somebody will buy the stupid things and it's a huge profit margin for them.
I say if AMD wants to keep focusing on Llano/Fusion, whatever, just make the parts available for desktop too if we want them. I don't, but for budget power they are not bad at all.
Fusion is huge and they'll probably be merging all their desktop parts into an APU design for the future, but that won't come until after Piledriver. I can't wait for the day that a single APU can provide enough power to play a demanding game at 1080p (or whatever the res will be then) without the need for a high end discrete GPU. Frankly, the fusion card is what AMD should be focusing on for well into the future and I guess the modular design of bulldozer actually helps in that respect because, assuming increased performance-per-module-per-watt, they'd be viable for the server space as well. The need for compilers is really what kills it, though.
The enthusiast market spent ~$10billion on parts last year. The enthusiast market is far from dead. The profit margins are higher in the enthusiast market and the advancements that are made there usually trickle down (or in the case of Intel, trickle up as well considering their xeons are essentially the same as SB desktop parts). It is slowing down in terms of growth rate whereas mobile is booming and all-in-one PCs are selling like hotcakes, but there's still a very large pool of $$ to be made there.