I suppose that if you’re upgrading to iPhone and already have one it is a waste to give you yet another charger. I wonder how much energy is used creating these cables that often go straight in a drawer because the previous cable is already conveniently plugged into the wall.
Yeah in theory it's a defensible move, because we're moving towards standardized charging ports. However, Apple is the only one that's being weird about it, introducing the Lightning connector instead of e.g. switching to micro-USB. USB-C was still a while out when Lightning was introduced. But honestly they have no excuse to not adopt Micro-USB or USB-C.
I expect Apple knows its customers would like to have confidence about this and that’s why they are holding off.
With Lightning, I have been happy enough to plug into various non-Apple-brand chargers with USB-A sockets. Maybe charging might not be as fast as with an official charger. But it will likely work and I don’t expect the possibility of damage.