App Tracking Transparency requires apps to get the users permission to track them.
Most users will opt out.
Take a look at the dialog below to see why.

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How Will Apple Block Tracking?
This is already on your phone.
These labels must be added whenever an app gets its next update.

Apple
From this alone, its pretty obvious that Google knows that nobody will opt into tracking.
What Will Happen To Google and Facebook?
Its important to note that Apple is not blocking anything with these new features.

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Its just giving the user information, and the ability to choose whether or not they allow tracking.
But the reason Google and Facebook are so scared is because they know what they do is bad.
Facebook is going on the offensive, and ispreparing an antitrust lawsuit against Apple.
One wonders what they hope to gain: after all, Apple is not actually blocking trackers here.