Why does LiveData only effect main layout and doesn't LiveData effect child layout UI in Android Studio?

FragmentHome load layout_home.xml, and layout_home.xml displays a recyclerview and a button named btnMain

recyclerview include the item layout layout_voice_item.xml, it displays a button named btnChild。

I use displayCheckBox : LiveData<Boolean> to control whether both btnMain and btnChild are shown or not with the code android:visibility="@{!aHomeViewModel.displayCheckBox? View.VISIBLE: View.GONE}".

I find btnMain can be shown or not when I change the value of displayCheckBox, but btnChild keep to show, why?

FragmentHome.kt

class FragmentHome : Fragment() {

    private lateinit var binding: LayoutHomeBinding

    private val mHomeViewModel by lazy {
        getViewModel {
            HomeViewModel(provideRepository(mContext))
        }
    }

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

        val adapter = VoiceAdapters(mHomeViewModel)
        binding.mvoiceList.adapter=adapter
        mHomeViewModel.listVoiceBySort.observe(viewLifecycleOwner){
          adapter.submitList(it)
        }
        ...
        return binding.root
    }
}

HomeViewModel.kt

class HomeViewModel(private val mDBVoiceRepository: DBVoiceRepository) : ViewModel() {

    private val _displayCheckBox = MutableLiveData<Boolean>(true)
    val displayCheckBox : LiveData<Boolean> = _displayCheckBox

    fun setCheckBox(isDisplay:Boolean){
        _displayCheckBox.value = isDisplay
    }

    ...
}

VoiceAdapters.kt

class VoiceAdapters (private val aHomeViewModel: HomeViewModel):
        ListAdapter<MVoice, VoiceAdapters.VoiceViewHolder>(MVoiceDiffCallback()) {
    ...
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VoiceViewHolder {
        return VoiceViewHolder(
            LayoutVoiceItemBinding.inflate(LayoutInflater.from(parent.context), parent, false)
        )
    }

    override fun onBindViewHolder(holder: VoiceViewHolder, position: Int) {
        val aMVoice = getItem(position)
        holder.bind(aHomeViewModel, aMVoice)
    }

    inner class VoiceViewHolder (private val binding: LayoutVoiceItemBinding):
          RecyclerView.ViewHolder(binding.root) {

        fun bind(mHomeViewModel: HomeViewModel, aMVoice: MVoice) {
            binding.aHomeViewModel = mHomeViewModel
            binding.executePendingBindings()
        }

    }

    ...
}
class MVoiceDiffCallback : DiffUtil.ItemCallback<MVoice>() {
    ...
}

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">

    <data>
        <import type="android.view.View" />

        <variable name="aHomeViewModel"
            type="info.dodata.voicerecorder.viewcontrol.HomeViewModel" />
    </data>

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

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/mvoice_list"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
            tools:listitem="@layout/layout_voice_item"            
        />

      <Button
            android:id="@+id/btnMain"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"         
            android:visibility="@{!aHomeViewModel.displayCheckBox? View.VISIBLE: View.GONE}"            
        />

</androidx.constraintlayout.widget.ConstraintLayout>
</layout>

layout_voice_item.xml

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

<data>
    <import type="android.view.View" />
    <variable name="aHomeViewModel"
        type="info.dodata.voicerecorder.viewcontrol.HomeViewModel" />
</data>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <Button
        android:id="@+id/btnChild"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:visibility="@{!aHomeViewModel.displayCheckBox? View.VISIBLE: View.GONE}"        
    />

</LinearLayout>
</layout>