As a whole, retail companies love the concept of gift cars as they get an instant flow of revenue regardless of whether or not customers actually use them before they expire or if they indeed make use of them. This mindset obviously also carries over to Apple's marketing strategy and mindset as well, but it does run deeper.
Back in the day, Apple offered physical gift cards that could be purchased at many retail outlets and grocery stores around the world, but each one was used for a specific Apple product or service such as Apple Podcasts, Apple Music or iTunes as well as the Apple Store and the iStore, however, this proved to be rather confusing to some and not as open to chose by the receiver. So, Apple scrapped that idea and made one universal gift card that can be used for anything Apple.
The gift card concept for Apple is highly beneficial as each time a customer receives an Apple gift card of value they fall deeper into the Apple ecosystem and are more and more unlikely to switch to another brand as their accumulated digital possessions are exclusive to Apple devices and products.
Take a look at the video below by the YouTube channel: Apple Explained on Why Apple Wants You To Buy Gift Cards...