"They already have lightning charging capabilities in their bedroom, in their car": The issue is not about the lightning end of things. It is the other end. I'm an iPhone user since 2007. Not having a USB-A_to_lightning solution in the box is super inconvenient. It would have cost Apple $2 to either include a split USB-C/USB-A cable or a small USB-A_to_USB-C adapter.
How is it inconvenient if, as you point out, you already have lightning infrastructure from the last 10 years of ownership? If anything, including usb-C to lightning is better for future proofing as it allows you to connect your phone to a new macbook for instance, which is capability you probably don't already have but may eventually need.
