Here's my personal conjecture based on owning most products in the Apple lineup and trying to predict the future a bit.
So far as I can tell the idea is Lightning ports for devices which require charging, and USB ports for devices which require data transfer.
All cables designed to provide power utilize a USB A connector - this is the majority of Lightning cables. In their current lineup this can be used to charge an iPad, iPhone, Apple Watch, and Air Pods case.
I recognize a lot of users still use the Lightning cable to transfer data to/from the phone to/from a computer. I'm betting Apple views these users as the current edge case.
Given that - it seems only a matter of time until an iPhone which has no ports, similar to the Apple Watch.
I imagine they'd rather not deal with USB-C on their devices at all - given the madness behind the different power capabilities of cables that seem to plague the specification. But they also recognize that is the future of general-use cables and are embracing it accordingly.
Given the lack of ability to charge any Apple peripheral directly from the newest Macbook (12" or Pro) models I suspect the internal rule is that devices with batteries aren't considered charging sources.
I'm personally excited to see the directions Apple keeps moving towards. I think it'll end up a more unified future than we've had yet. But I'm also ready to be wrong. I'll try to look back on this in a few years and see how we are.