When future search engines begin receiving feedback from users and ranking accordingly Google will become irrelevant.
Wrt to Search,
Scale: Huge cost of infrastructure, data is privatize.
You could run a hobby scale pagerank but for searching web it would be a needle in a haystack.
They have competition like yandex, nacy, baidu but are not for English web and not open source
For instance, if Microsoft controlled them, they could just point the search functionality toward Bing, and most users mightn't even notice.