Why? No idea. It's a much slower standard, and puts the wearing parts in the port instead of the cable. USB-C is designed by committee, sure, but the port itself is better than lightning in nearly every consumer metric there is.
USB-C exists because Apple was in the process of creating Lightning. Also, in my experience, you seem to have the fragility point backward: the nub on lightning cables may break, but the port is fine, while the reverse is true for USB-C, where the fragile bit is in the port.
Beyond that, the springloaded contacts are on the cable end with type-c, with lightning it's inside the phone. I don't think it's a particularly common failure mode, but having less moving parts in the expensive bit is generally a good idea.