How dependency injection in Angular is useful since it doesn't solve anything apparently?

How this can improve my code? How it can remove dependency ? I still don't see any benefit of using this ?

@Component({
selector: 'talk-list',
templateUrl: 'talks.html',
providers: [TalksAppBackend]
})
class TalkList {
constructor(backend:TalksAppBackend) {
this.talks = backend.fetchTalks();
}
}


If i had used

TalksAppBackend t= new TalksAppBackend(); that would have been the same. Apart from syntactical difference how different it is?

Update:

Also, it's calling .fetchTalks(); that's not mocking. How its possible?

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