Why is it so difficult to built a competitive search engine next to Google and Bing?

Isn't it possible to "find" the most valuable website in the web with the help of a well mixed community? I am thinking if an small browser add-on which can share the basic url of a visited websites with a website scrapper. The scrapper can then index the whole website with its sub pages. The add-on could be installed independently by users which would like to strengthen the network.

Besides setting up an own search index, one could try to export search results from #Google and Bing as a ramp up help, which are similar to #startpage and #duckduckgo. I mean I am no search engine expert, but is there so much more magic?