because their current lighting cable only transfers at USB 2.0 speeds as well

This is the main reason. People are confusing the protocol (USB 2.0/3.0) with the connector (USB C/Lightning). Apple slapping a different connector on the phone isn't changing the underlying technology inside the phone. People claiming that USB-C must mean 3.0 are just spreading FUD in order to shit on Apple again.

And, as others in this thread have pointed out, high speed transfers by cable are low priority for phone users, there are much better tools to do that, like maybe an external hard drive.

The current implementation uses the same electrical wiring as USB 2.0 and they used it because at the time USB-C 2.0 hadn't been released yet. Fair enough, but that was a decade ago, so there's no reason that they haven't upgraded in that time except they realised that it let them sell an inferior cable for more money and tell everyone it was better than USB-C standard. The thing is, if you're moving over to USB-C now anyway why not also take the opportunity to upgrade to 3.0 speeds?

It would cost them literally nothing to do that, and they're still not doing it. Well at the same time they're going on and on about how amazingly fast their wireless charger is. Seems suspicious.