Starting & Stopping the Drive through Digital Outputs of the PLC

Good afternoon.
On the lesson ( Starting & Stopping the Drive through Digital Outputs of the PLC) for PowerFlex 525 VFD, why is the output of the PLC use to turn on the VFD.
(input 02 of the VFD) DigIN TermBlk02/ Start/Run REV is connected to the output of the PLC, why is that?

also can one of the input terminals be use instead of the output?

The output of the PLC is connected to the input of the drive. You can’t use an Input for that. In other words, it must respect the [PLC - Output] → [Drive - Input] OR [PLC - Input] ← [Drive - Output]