Basically, I blame the system. In a bike companies' quest to try and sell you a different bike every year, they have to come up with something - anything - new. So, bonding a bit of carbon for a seatstay achieves a few things -

1) It's easy to bond in a one piece assembly - no PITA seatstays to mitre and weld in there. You don't even have to be that accurate with the bonding. You should see the instructions you get with these things. In a word - dodgy.
2) It tends to save about 40g-60g compared to steel stays. Apparently that means a lot to some people. Personally I'd rather save that in the wheels, and have a frame with structural integrity.
3) Everyone is under the impression CF has some magical damping properties, which I've never seen quantified. People keep believeing it though. If you want damping, get a sloping top tube frame that exposes more seatpost, take 5psi out of your already over inflated tires, double wrap your bars, and buy a seat that is actually comfortable. *BAM* - Instantaneous more damping than glueing a bit of CF into the stays will ever produce.

Of course, none of this will satisfy the consumers' lust for anything that vaguely carries the illusion of being 'high tech' or 'high performance'. Most people will keep eating the same old **** and believeing whatever their told, regardless of the reality.

Makes me wonder - as a product manager for a large bike company, you'd have to have borderline contempt for the human race, wouldn't you? How could you not? It's a pretty simple formula to keep the plebs chomping at the bit and extolling the rhetoric.

Ah man, I feel another Bill Hicks quote coming on....someone stop me