I believe that your problem is caused by the fact that USB is a master/slave system, meaning that there is a master (usually a computer) that sends and receives data to various slave units. As a result, there is no THRU concept.

It is conceivable that you could run an application of the computer that would receive data from one slave and send it to another – this would appear to give a THRU operation. But, while possible, this would be rather unusual, and would probably come with its own share of problems.

Both of the above are very different from DIN MIDI which sends stuff to a receiver, which can then send stuff to another receiver ad infinitum  in a "daisy-chain" fashion, without any master unit.