Why I need to explicitly add the fragment and activity dependencies in android?

Question

I don't understand, while learning through a codelab in android they want me to add the following dependencies to the android build.gradle

implementation "androidx.activity:activity-ktx:1.4.0"
implementation "androidx.fragment:fragment-ktx:1.4.1"

But I am not able to figure out what difference does it create?

Link to the code lab: https://developer.android.com/codelabs/android-app-permissions#6