Because it breaks down if we use another example. Would you want to solve a rubik's cube that was pre-turned so there were only 3 flips left to complete the cube? Changing the state of the activity (adding bolts/belays/ladders/etc.) is not in the spirit of the event, just as almost finishing a rubik's cube for someone else isn't in the spirit of actual event.

Put a different way: the climb becomes the bolter's experience, not the mountain's experience. It is no longer intrinsically mountain climbing, it's hiking.

>Would you want to solve a rubik's cube that was pre-turned so there were only 3 flips left to complete the cube?

Well no, but I wouldn't get mad if someone else wanted to.