Because Thunderbolt is basically an extension of the PCI bus. This means that the protocol _is_designed_ to grant full memory access to external devices (in fac

Because Thunderbolt is basically an extension of the PCI bus. This means that the protocol _is_designed_ to grant full memory access to external devices (in fact that's the way how the DMA data transfer in Thunderbolt works). With other protocols such as USB or DisplayPort you don't have those issues. Of course, a faulty driver could be used to compromise the system, but the protocol itself is secure.