[deong]

Yahoo! didn't switch their vision from a search engine. Yahoo! was a portal long before it was a search engine. In ye olden times, Yahoo! maintained a curated list of hierarchically organized links. That was their core product.

I would argue that Yahoo! lost to Google because Yahoo!'s business was in approximating a solution to a problem that users had, and Google came along and figured out a way to much more directly address that problem. Curated lists were better than nothing, and for a long time, it was the best thing available. Google simply built a new type of thing that made the old way immediately obsolete.