Not sure why. It's not crazy compression and it will bleed off plenty of cylinder pressure at lower RPMs. TIming will be key. Most guys have too much timing and way to fast of a curve for street use.
Experience. With that combination, and the way I calculate dynamic compression, it's nearly 9:1. I like the dynamic lower with pump gas. Everyone is free to run the way they want. I'd rather be safer than fight detonation.