My understanding of the Thunderbolt technology is that it is just another newer type of USB connection.
Well, no. Thunderbolt and USB 3 are complementary technologies, architected differently for different roles. USB is for low-speed low-priority communication, while Thunderbolt is for high-speed high-priority communication. USB depends on available CPU power, Thunderbolt does not. Because they have different roles, Intel puts both on the latest motherboards.
It has always been this way. On the first Macs, SCSI was the fast standard and ADB was the slow one. On recent Macs, FireWire was the fast self-hosted standard and USB was the slow one that depended on and burdened the CPU.
Because their roles were clear, nobody ever asked for a SCSI mouse or FireWire keyboard. Jobs like that were for USB.
USB 3 is finally fast enough to do the consumer jobs that used to require something like SCSI or FireWire, like connect fast hard drives. Most consumers won't ever have a real need for Thunderbolt. But now there are even bigger jobs to be done by professionals, like producing 4K video, and even USB 3 can't handle that. So Intel came out with Thunderbolt.
Lightning is Apple's own slow bus (used instead of USB) for mobile, low-power devices so once again nobody is going to ask for a Thunderbolt-to-Lightning iPhone cable because it doesn't make any more sense than asking for a Thunderbolt mouse.
I suppose it could be possible to build a cable that translated between USB and Thunderbolt, but the very low level of chatter on the web about it means that you are probably much better served by buying a USB hub than waiting for a cable that will let you use low-end USB-type devices on the Thunderbolt ports.