How Personalization Changed Digital Marketing in 2021
The year Apple's App Tracking Transparency prompt went live and personalization had to rebuild itself around data customers gave willingly.
On April 26, 2021, Apple rolled out App Tracking Transparency with iOS 14.5, requiring every app to show an explicit prompt asking permission before tracking a user across other companies’ apps and websites. The overwhelming majority of users declined it. That single prompt did more to change how personalization worked in practice during 2021 than any new personalization technology released that year.
Why this hit personalization specifically, not just ad targeting
Most coverage of App Tracking Transparency focused on advertising measurement, and Meta itself later told investors the change had cost the company billions in revenue. But personalization systems built on the same cross-app behavioral signals were affected just as directly, because a lot of personalized product recommendations and content targeting quietly relied on the same tracked behavioral data that powered ad targeting. When that visibility dropped, personalization engines that had been inferring interests from browsing behavior across other apps lost a meaningful share of their input overnight.
Google’s own delay added to the uncertainty
In June 2021, Google pushed back its plan to phase out third-party cookies in Chrome, moving the original two-year timeline further out. For personalization teams that had spent the prior year building roadmaps around a fixed deadline, this didn’t restore what App Tracking Transparency had already taken away, but it did mean the web side of the cookieless shift was less urgent than the mobile side had just become, which shifted a lot of 2021 personalization budget toward first-party data collection rather than waiting out the browser timeline.
What personalization shifted toward
With cross-app tracking sharply reduced, the personalization that kept working in 2021 was built on data customers gave directly and knowingly: purchase history, on-site browsing behavior on a business’s own properties, loyalty program activity and explicit preferences collected through quizzes or account settings. This wasn’t a new technique, but it went from being one input among several to being the primary one for a lot of teams that had previously leaned on third-party behavioral data as a shortcut.
Retail media became the workaround
Retailers with large first-party purchase datasets, most visibly Amazon but also newer entrants like Walmart Connect, which launched its retail media offering in 2021, became an increasingly attractive place to advertise precisely because they had first-party signal that wasn’t affected by App Tracking Transparency or browser cookie policy. Brands that couldn’t personalize their own targeting as precisely as before started buying into these retail media networks specifically to reach people through data the retailer owned directly.
What changed for good
The businesses that adjusted fastest in 2021 treated the App Tracking Transparency rollout as confirmation of a direction rather than a one-off disruption to route around. Personalization that depended on tracking people across properties a business didn’t own turned out to be fragile in exactly the way privacy advocates had warned it would be, while personalization built on a business’s own customer relationship kept working through the disruption largely unaffected. That distinction, whose data it was, turned out to matter more in 2021 than any algorithm running on top of it.
