Very recently, an interesting event took place. Twitter for iOS announced that users must allow tracking for more relevant ads. Twitter seems to be very clear in its intentions. This is exactly what they mentioned, as pointed out by Macrumors:
Keep ads relevant to you by allowing Twitter to track data from other companies on this device, like apps you use and websites you visit.
[…] You can decide if you’ll allow tracking in the iOS prompt and you can always change this later in your device settings.
Facebook has always spoken against this app tracking transparency, because they think it takes a toll on small businesses and refrain them from reaching their target audience. You must have seen the vigorous ads cluttering your Facebook news feed and messengers. This is because the apps track you’re web activity, apps you download, products you search on the internet browsers, etc. Facebook and other social media platforms even thought of various tactics, such as making the apps paid services if they cannot earn from Ads.