because many players base their speed on their very best game, and not their average game, so they have an inflated opinion of their skill.
Why do people that have no business trying to give weight try to? I was playing a guy the other day that I should have been playing even but he was was trying to give me the seven. Why? Is it an ego thing? Maybe an excuse if they loose "well I was giving him this". I don't know. What I do know is that I hope I keep running into these people. Any ideas?