Why using the factory pattern when a simple dependecy injection is enough

Im looking to this example to understand the use of factory pattern.

I'm really amator in this field so excuse my silly question.

My problem is that i don't see the use of the factory pattern which return us the interface that we can inject it directly when we need to use it.

In the example above I would do something like this:

public class Program
{
    // register the interfaces with DI container in a separate config class (Unity in this case)
    private readonly IShippingStrategy _shippingStrategy;

    public Program(IShippingStrategy shippingStrategy)
    {
        _shippingStrategy= shippingStrategy;
    }

    public int DoTheWork(Order order)
    {
        // assign properties just as an example
        order.ShippingMethod = "Fedex";
        order.OrderTotal = 90;
        order.OrderWeight = 12;
        order.OrderZipCode = 98109;

        int shippingCost = _shippingStrategy.CalculateShippingCost(order);

        return shippingCost;
    }
}

Instead of injecting the factory :

public class Program
{
    // register the interfaces with DI container in a separate config class (Unity in this case)
    private readonly IShippingStrategyFactory _shippingStrategyFactory;

    public Program(IShippingStrategyFactory shippingStrategyFactory)
    {
        _shippingStrategyFactory = shippingStrategyFactory;
    }

    public int DoTheWork(Order order)
    {
        // assign properties just as an example
        order.ShippingMethod = "Fedex";
        order.OrderTotal = 90;
        order.OrderWeight = 12;
        order.OrderZipCode = 98109;

        IShippingStrategy shippingStrategy = _shippingStrategyFactory.GetShippingStrategy(order);
        int shippingCost = shippingStrategy.CalculateShippingCost(order);

        return shippingCost;
    }
}

Why taking the bruden to create a factory (thus adding an extra layer) when we can inject the interface directly to wherever we need to use it ?