wpf - StackPanel の可視性とグリッドの可視性

Question

MVVM アプリケーションを使用していますが、理解できないことがあります。StackPanel の可視性とグリッドの可視性の違いは何ですか。このグリッドがあれば...

 <UserControl x:Class="Envitech.Setup.Presentation.Views.MonitorScreenViews.MonitorAlertViews.MonitorAlertView" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  xmlns:d="http://schemas.microsoft.com/expression/blend/2008" mc:Ignorable="d" d:DesignHeight="438" d:DesignWidth="842" xmlns:popup="clr-namespace:Envitech.Setup.Presentation.Views.GlobalViews">
    <DockPanel DataContext="{Binding MonitorAlertViewModel}" Width="824" HorizontalAlignment="Left" VerticalAlignment="Top" Height="435">                        
        <Grid DataContext="{Binding CurrentMonitorAlert}" Height="422" Visibility="{Binding Path=NoMonitorsMessageVisibility, Converter={StaticResource visibilityConverter}}">
            <Label Content="Value" Height="28" HorizontalAlignment="Left" Margin="10,103,0,0"  VerticalAlignment="Top" />            
        </Grid>
    </DockPanel>
</UserControl>

可視性は機能しませんが、このようにすると...

 <UserControl x:Class="Envitech.Setup.Presentation.Views.MonitorScreenViews.MonitorAlertViews.MonitorAlertView" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  xmlns:d="http://schemas.microsoft.com/expression/blend/2008" mc:Ignorable="d" d:DesignHeight="438" d:DesignWidth="842" xmlns:popup="clr-namespace:Envitech.Setup.Presentation.Views.GlobalViews">
    <DockPanel DataContext="{Binding MonitorAlertViewModel}" Width="824" HorizontalAlignment="Left" VerticalAlignment="Top" Height="435">                
        <StackPanel Visibility="{Binding Path=NoMonitorsMessageVisibility, Converter={StaticResource visibilityConverter}}">
        <Grid DataContext="{Binding CurrentMonitorAlert}" Height="422">
            <Label Content="Value" Height="28" HorizontalAlignment="Left" Margin="10,103,0,0"  VerticalAlignment="Top" />            
        </Grid>
        </StackPanel>       
    </DockPanel>
</UserControl>

可視性は問題なく機能します。

なんで？