Facebook exists for one reason: to make money selling targeted advertising. That's it. Anything that prevents Facebook from tracking what its users do online — the websites they visit, the videos they watch, the posts they "like," the things they buy — is going to put a kink in its cash hose.
That's why Facebook (and many other websites) hate the iOS 14.5's pop-up that makes it dead simple to opt-out of being tracked. Look at it. How many people are going to click "Allow 'Facebook' to track your activities across other companies' apps and websites?" Not many, I'll wager.
Also from Protocol:
Expect the next phase of app development to focus on keeping users inside of an app for as long as possible. If all Facebook can collect is first-party data, you better believe it's going to find as many creative ways to keep you in the Facebook app as it possibly can.
Facebook and others built big businesses on being portals to everything, because users and data always flowed back. Now, I suspect we'll see their walls get higher, their platforms more all-consuming and their reasons to let you leave start to dwindle.