Key Lookup isn’t applied by default?

I’m trying to learn about covering indexes. In the Northwind database, I select from the table Categories:

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As you can see the table has a non-clustered index on the column CategoryName.

This SQL query:

select CategoryName  from Categories where Categories.CategoryName like 'Beverages' 

returns an execution plan with an index seek:

enter image description here

However, this:

select CategoryName ,Description from Categories where Categories.CategoryName like 'Beverages' 

returns this execution plan with an index scan using the primary key index, which isn’t expected:

enter image description here

I can find the expected behaviour only when I force the query with the non-clustered index:

 select CategoryName ,Description from Categories     with(index(CategoryName))  where Categories.CategoryName like 'Beverages' 

enter image description here

What is the problem?