Most guys tap when they first scream that kind of ugly noise.
My guess is the unified rule makers don't want that noise persisting in viewers ears while watching this sport. Kind of funny but it's been like that for a while.
The logic for this is the same as the visual cue on Tim Sylvia's broken arm ,the difference is you can't see a torn knee ligament so they go with an auditory cue.
Does it seem panzy? Yes, but the guys who "will never tap" might end up with zero ligaments left in their knee and just scream through the entire process.
Especially if one move passes them into shock, they may not be able to tap.