Why are there two thresholds on the Drumstrip gate?
The two thresholds, open and close, give you more control over the behaviour of the gate. The open threshold controls where the gate will open on the attack portion of a drum hit. The close threshold allows you to set where the gate will close on the decay portion of a drum hit.
A gate with a single threshold control will usually combine these controls with a fixed amount of hysteresis between them.