^ this. your browser is a user agent, it's working for you, to protect you from any schmuck who you have the misfortune of visiting. it has strict built-in privacy and security guarantees, which, while in no way interfere with the app's primary functionality, do interfere in their marketing bullshit and other kinds of spying.
with apps, you have none of that protective layer, instead there is a certain degree of implied trust which these parties love to abuse.