Because lightning doesn’t even support anything. Half the things you might plug in a cable for, like video out, are implemented by a chip in the cable itself (which means you still need to buy specific cables for specific jobs), and lighting doesn’t even have the bandwidth to provide real video out at an iPhones screen resolution, let alone operate at 40Gbps. Moreover you have exactly the same issues with lightning charging cables, if you buy the wrong one it will not charge at the desired rate [1].

Lightning does not come close to solving these problems.

[1] https://gtrusted.com/what-happens-when-you-use-the-original-...