Why doen't CoordinatorLayout release space for Snackbar messsage in Android Studio?

I know that CoordinatorLayout will release some space and let Snackbar display message at the bottom of screen normally.

In the following code, the AppCompatActivity layout layout_main.xml load a Fragment layout layout_home.xml.

layout_main.xml is CoordinatorLayout, I think the CoordinatorLayout will release space for Snackbar messsage when I click btnStart button.

But in fact, the CoordinatorLayout doesn't release space for Snackbar messsage, you can see Image A.

What is the problem with my code?

ActivityMain.kt

class ActivityMain : AppCompatActivity() {

    private lateinit var binding: LayoutMainBinding  
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this, R.layout.layout_main)

    }
}

FragmentHome.kt

class FragmentHome : Fragment() {

    private lateinit var binding: LayoutHomeBinding

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        binding = DataBindingUtil.inflate(
            inflater, R.layout.layout_home, container, false
        )

        binding.btnStart.setOnClickListener {
            Snackbar.make(binding.btnStart, "This is main activity", Snackbar.LENGTH_LONG)
                .setAction("CLOSE") {
                }
                .setActionTextColor(resources.getColor(android.R.color.holo_red_light))
                .show()

        }

        return binding.root
    }
}

layout_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <androidx.coordinatorlayout.widget.CoordinatorLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.google.android.material.appbar.AppBarLayout
            android:id="@+id/appbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fitsSystemWindows="true">

            <androidx.appcompat.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?android:attr/actionBarSize"
                android:background="@color/colorPrimary"
                android:theme="@style/ThemeOverlay.MaterialComponents.Dark.ActionBar"
            />

        </com.google.android.material.appbar.AppBarLayout>

        <fragment
            android:id="@+id/fragment_navigation"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"
            app:defaultNavHost="true"
            app:navGraph="@navigation/nav_graph" />


    </androidx.coordinatorlayout.widget.CoordinatorLayout>

</layout>

layout_home.xml

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

<androidx.constraintlayout.widget.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/btnStart"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="Start"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

</layout>

Image A

from Why doen't CoordinatorLayout release space for Snackbar messsage in Android Studio?