The unfortunate thing is that Thunderbolt was created, and instead of a simple way to make PCIe external, we have this Intel-created mess that tunnels PCIe over some cursed "MPLS-like network" or whatever it is. And it was completely Intel-proprietary until recently. At least now the spec is open.
We should have different connectors for different data rates and power levels. Don't pass the buck to designers, they'll screw up.
Ok, sarcasm aside. Technicaly you dont need separate plugs for different connection levels and power transmission up to certain powers. Initial data exchange at some base speed and minimum power requirements can provide necesarry information for devices to establish or refuse connection
And it's still only useful for low power devices.
I've never gotten a real answer, one that involves technical reasons. It could be done, but it isn't.
I guess people like having different kinds of cables?