The answer has to do with the enormity of the social networks, the complexity of catching fakes, and the business incentives of the companies that run the sites. 

Facebook said it blocked 4.5 billion accounts in the first nine months of the year, and that it caught more than 99 percent of those accounts before users could flag them. That number of accounts — equivalent to nearly 60 percent of the world’s population — is mind-boggling. It’s also inflated. The vast majority of those accounts were so-called bots, or automated accounts that are often created en masse by software programs. Bots have been used for years to artificially amplify certain posts or topics so they are seen by more people. 

In recent years, Facebook, Twitter and other tech companies have gotten much better at catching bots. They use software that spots and blocks them, often during the registration process, by looking for digital evidence that suggests the accounts are automated. 

As Facebook has caught more bots, it has also reported increasingly colossal statistics on how many fake accounts it takes down. Those numbers have brought the company plenty of positive headlines, but “they’re actually not used internally that much,” said Alex Stamos, Facebook’s former chief information security officer, who left the company in 2018. “One person can blow out the stats, because there’s no cost to do an attempt.” 

In other words, one person can create a software program that attempts to create millions of Facebook accounts, and when Facebook’s software blocks those bots, its tally of deleted fakes swells. Facebook has admitted that these statistics are not that helpful. 

“The number for fake accounts actioned is very skewed by simplistic attacks,” Alex Schultz, Facebook’s vice president of analytics, said last year. The prevalence of fake accounts is a more telling metric, he said. And it shows the company still has a big problem. 

Despite removing billions of accounts, Facebook estimates that 5 percent of its profiles are fake, or more than 90 million accounts, a figure that hasn’t budged for more than a year. The social media companies have a much harder time with fake accounts that are created manually — that is, by a person sitting at a computer or tapping away on a phone. 

Such fakes don’t carry the same tell-tale digital signs of a bot. Instead, the companies’ software has to look for other clues, like an account sending multiple strangers the same message. But that approach is imperfect and works better for certain kinds of fakes. 

That in part explains why Josh Hall, the Pennsylvania delivery driver, was able to repeatedly impersonate President Trump’s relatives on Twitter and attract tens of thousands of followers before the company took notice. Manual fakes can be more pernicious than bots because they look more believable. 

Political operatives use such fakes to spread disinformation and conspiracy theories, while scammers use them to defraud people. Criminals have posed as celebrities, soldiers and even Mark Zuckerberg on social media to trick people into handing over money. 

Twitter’s effort to catch impostor accounts is complicated by its policy allowing parody accounts. 

The company requires parody accounts to be clearly labelled. Facebook also still struggles with accounts that pose as those belonging to public figures, but periodic reviews by The New York Times suggest the company has gotten better at removing them. Instagram, which Facebook owns, has not made as much progress.