The report says that Apple’s motivation to build out its own infrastructure came after a conversation with Microsoft. Microsoft won’t be able to handle Apple’s continued growth in the cloud, meaning that Apple would have to aid Microsoft in growing Azure. So in the long run, it makes much more sense for Apple to work on building out its own networks rather than supporting Microsoft’s.
Apple has also been buying up land in China and Hong Kong to build out data centers, according to the report, although specific details are unclear.