Given two models:

public class Person
{
    public Address Address { get; set; } = null!;
}
public class Address
{
    public string City { get; set; } = null!;
}

And a page:

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();
        BindingContext = new Person
        {
            Address = new Address { City = "New York" }
        };
    }
}

<Label Text="{Binding}" BindingContext="{Binding Address.City}" />

The above code works as expected but why can’t it be rewritten as follows?

<Label Text="{Binding City, Source={Binding Address}}" />
<Label Text="{Binding}" BindingContext="{Binding City, Source={Binding Address}}" />