I don't know the thing with threading to me is that it always struck me as being legal from my understanding of the law.

For instance, if I'm in a car, and a car in front of me is obstructing the lane and there's room for me to pass while still in the lane, I can legally do so.

So if I'm on my bike, which is defined as a vehicle, and a car is in front of me obstructing my lane, why can't I pass it exactly? If I'm on the right of the lane divider, I'm passing an obstruction within my own lane. What's illegal about that?