Sure, iPhones now ship with a USB-C to Lightning cable. But all of the USB-A to Lightning cords and USB-A chargers, which most iPhone users have way more of, will still charge your iPhone, albeit not as fast as a USB-C charger would. I think most people would rather gain a fast charger and have all of their slower chargers and cables still work than get a fast charger and have to throw away and buy replacements for all their other chargers and cables.