The reason I used my syntax is quite simple - it's used throughout CoreBundle/Checkout/Step classes. Examples:

AddressingStep: https://github.com/Sylius/Sylius/blob/master/src/Sylius/Bundle/CoreBundle/Checkout/Step/AddressingStep.php#L52

SecurityStep.php: https://github.com/Sylius/Sylius/blob/master/src/Sylius/Bundle/CoreBundle/Checkout/Step/SecurityStep.php#L71