TV advertising in the United States is worth more than $60 billion a year. And much of those ad sales hinge on Nielsen ratings. But Nielsen hasn’t kept up with the changes in how people watch TV — until now. The marketing firm plans to remake its measurement system to finally include streaming by 2024. So why did the move take so long, and why now?

Every day, thousands of families across the country let Nielsen into their homes through a little box connected to their TVs. They’re dripping data straight to Nielsen through that little black box, and that’s how advertising rates are set. The problem is, a lot of people don’t watch TV on TVs.

“The reality is that consumers’ viewing behaviors have been changing very rapidly over the last 10 to 15 years,” said Tim Hanlon, CEO of The Vertere Group, a media and tech consulting firm.

We’re watching on phones, laptops and tablets. So why the lag in tracking these viewers? Because in the beginning, streaming was dominated by subscription platforms like Netflix and Amazon.

“Neither of them sell ads, so they’ve not had an interest in paying to get this type of programming measured,” siad Brian Wieser, a media analyst with GroupM.

Then streaming got so big that networks like NBC and ESPN launched their own platforms. And here we are, with commercials over the internet where advertisers can deliver hyper-targeted ads. You know where else hyper-targeted ads run with much better data? Google Search, Instagram and TikTok. And Martin Block, professor of integrated marketing at Northwestern University, said advertisers are getting impatient.

“I think it’s in response to competition from things digital,” he said.

The thing is, Nielsen’s new measurement system won’t fully roll out until 2024. It may be a good tracking tool, but think about it: TikTok has been around for about four years. Things change — fast.