Google has 68% of the market of web searches in America and more than 90% in many European countries. Like Facebook, Amazon and other tech giants, it benefits from the network effects whereby the popularity of a service attracts more users and thus becomes self-perpetuating. It collects more data than other company and is better at mining those data for insights. Once people start using Google's search (and its e-mail, maps and digital storage), they rarely move on. 

There are good reasons why governments should regulate internet monopolies less energetically than offline ones. 

First, barriers to entry are lower in the digital realm. It has never been easier to launch a new online product or service: consider the rapid use of Instagram, WhatsApp or Slack. Building a rival infrastructure to a physical incumbent is far more expensive, and as a result there is less competition in the real world. True, big firms can always buy upstart rivals(as Facebook did with Instagram and WhatsApp, and Google did with Waze, Apture and many more). But such acquisitions then encourage the formation of even more start-ups, creating even more competition for incumbents. 

Second, although switching from Google and other online giants is not costless, their products do not lock customers in as Windows, Microsoft's operating system, did. And although network effects may persist for a while, they do not confer a lasting advantage: consider the decline of MySpace, or more recently of Orkut, Google's once-dominant social network in Brazil, both eclipsed by Facebook - itself threatened by a wave of messaging apps. 

Finally, the lesson of recent decades is that technology monopolies(think of IBM in mainframes or Microsoft in PC operating systems) may be dominant for a while, but they are eventually toppled when they fail to move with the times, or when new technologies expand the market in unexpected ways, exposing them to new rivals. Facebook is eating into Google's advertising revenue. Despite the success of Android, Google's mobile platform, the rise of smartphones may undermine Google: users now spend more time on apps than on the web, and Google is gradually losing control of Android as other firms build their own mobile ecosystems on top of its opensource underpinnings. So far, no company has remained information technology's top dog from one cycle to the next. Sometimes former monopolies end up with a lucrative franchise in a legacy area, as Microsoft and IBM have. But the kingdoms they rule turn out to be only part of a much larger map.