SwipeGestureRecognizer not working

Perhaps I'm not understanding how to implement?
see repo here:
https://github.com/InquisitorJax/Xamarin-Forms-Shell

sample code

    <Grid>
            <StackLayout Margin="10,0,10,20">
                <!--  Place new controls here  -->
                <Label HorizontalOptions="Center"
                       Text="Welcome to Xamarin.Forms!"
                       VerticalOptions="CenterAndExpand" />

                <Button BackgroundColor="#FF5500"
                        Command="{Binding NavigateToItemPageCommand}"
                        CornerRadius="25"
                        Text="Navigate to Item Page"
                        TextColor="White" />


            </StackLayout>
            <Grid.GestureRecognizers>
                <SwipeGestureRecognizer Direction="Left" Swiped="SwipeGestureRecognizer_Swiped" />
                <SwipeGestureRecognizer Direction="Right" Swiped="SwipeGestureRecognizer_Swiped_1" />
            </Grid.GestureRecognizers>

        </Grid>

The event handlers aren't firing on swipe.