Before I delve into why Lightning is more robust...some info about me.
Prior to buying the 6s last Oct, I had never owned a smartphone. And prior to May 2016, I never had a device that featured mini-USB either.
All this is to impress upon you that I had no experience with Lightning, or the mini-USB, or USB-C either for that matter. The three most common connector types being used today were totally foreign to me.
So the thing that struck me deeply upon seeing my iPhone was how robust the Lightning connector is.
Much of that is due to the fact that it's a -female- connector. No pins to break off or in danger of bending. To charge your phone or iPad, a male plug is to be inserted. The male plug may break off inside, but once extracted...the female connector is still intact and unharmed. The force needed to crack the female socket is pretty considerable.
In contrast, the mini-USB on phones/tablets is a male connector...much more prone to damage by insertion, bending, rough handling, etc. It's ridiculous how easy it is to damage the male connector.
And now w/the USB-C, it is no better. Same weakness. It's actually very disappointing that they never switched to a female connector, still.
If Apple keeps the iPad/iPhone on Lightning, I for one will continue be very happy. The less I see of USB-C in this regard...the better.