A surprise for me was that lightning is only USB2 and one-sided, so at any moment it is plugged half of the pins is unused. Additionally it has exposed wires, in case of charger failure, USB-C provides a better protection.
The exposed wires make lightning easier to plug into a phone than USB-C: you don’t have to line up the lightning connector with its port as precisely as you do USB-C because the connector is slightly smaller than the port, whereas it is almost flush in USB-C.
Some Lightning devices use both sides to get USB3 speeds. I really have no idea why Apple have left other devices at USB2 performance. It doesn't make an awful lot of sense to me.
Because what's their incentive to do better? Most people only use the port for charging, which has no data speed, and the number of people who sync via wire is lower than ever and declining. USB2 was good enough for a long time, and it's not like it changed.
I expect Apple to do away with the lightning port eventually and just ship MagSafe (the phone kind) chargers with their phones for a completely wireless phone with no holes at all. We aren’t there yet (many people still like wired headphone solutions vs Bluetooth), but maybe in 2-3 years?
At the same time, it is starting to look like USB-C is still not going to be more robust than Lightning connectors. A vast improvement on micro USB, to be sure, but still. Recall that Lightning came out 12 years ago, and the alternative was micro-USB. It's so much better that we can actually debate it relative to USB-C today, which is high praise.