Building a web index and search service to compete with Google requires huge capital expenditures and going up against a network effect that Google exerts on the market (often by paying other companies to be the default). The only company to marginally succeed is Microsoft, and virtually every other search service uses Bing's index on their backend. The cost of switching is low but the barriers to participating meaningfully in the market are high.

How is search a network effects business? It seems to me that each additional user would contribute less than the previous one, as opposed to Metcalfe's law (where each additional user adds more value than the last). How would paying to be a default be a network effect? Perhaps the capital cost to competing with Google is high, but if it were worth it, there are a number of firms which could afford it; it seems like it's just not worth it.