From Mat Honan at Gizmodo, an account of how Yahoo bought Flickr and then frittered away all its potential.
Because Flickr wasn’t as profitable as some of the other bigger properties, like Yahoo Mail or Yahoo Sports, it wasn’t given the resources that were dedicated to other products. That meant it had to spend its resources on integration, rather than innovation. Which made it harder to attract new users, which meant it couldn’t make as much money, which meant (full circle) it didn’t get more resources. And so it goes.
As a result of being resource-starved, Flickr quit planting the anchors it needed to climb ever higher. It missed the boat on local, on real time, on mobile, and even ultimately on social-the field it pioneered. And so, it never became the Flickr of video; YouTube snagged that ring. It never became the Flickr of people, which was of course Facebook. It remained the Flickr of photos. At least, until Instagram came along.