I think what really killed the adventure genre was that technology advanced to the point that action games became viable. I think people in general prefer action to thinking, particularly when they're trying to unwind, relax, have a good time. To be honest, I'm not entirely convinced that the market for adventure games every dried up very much, but rather the overall videogame market expanded tremendously, but the adventure game market stayed fairly static. So an adventure game might sell the same as much today as it ever would have, but what used to be an enormous success, say selling 250,000 copies of a videogame, is now considered an abysmal failure.
Adventure games never got sucky, I don't think. The market demographics just changed.