That’s the way Epic mapped the Oculus Touch input.
“MotionControllerGrip 1 Axis” = Oculus Touch “Hand Trigger” and also HTC Vive Grip left
“MotionControllerGrip 2 Axis” = nothing Touch but HTC Vive Grip right
I’m working with 4.15 right now and you can map directly the Oculus Touch inputs. However I did it this way to facilitate mapping visually the input for each controllers