ICarrierProvider CanDeliver

Following this example from the docs:

https://docs.kentico.com/display/K9/Example+-+Creating+a+shipping+carrier+provider+with+costs+based+on+the+country

I'm creating a custom Shipping Carrier Provider. I have the following in the CanDeliver() method:

public bool CanDeliver(Delivery delivery)
{
    EventLogProvider.LogInformation("USPSCarrierProvider", "CanDeliver", "Shipping Option: " + delivery.ShippingOption.ShippingOptionName);
    return false;
}

The log information never gets written and the shipping options (there are two services defined in the GetServices() method) still show up in the shipping selector in my checkout process.

The rest of the provider seems to work fine, i.e. it calculates shipping costs fine.

Help. Thanks!