Because Extreme Speed has +2 Priority, beating out Sucker Punch.
There is a reason extreme speed should beat out sucker punch
Not a good one.
Do you know what a sucker punch is?
If i'm ready for your surprise attack won't it make sense to fail -_-. It's a cheap shot while your opponent is making a move, if i'm using extreme speed i'm easily going to get around your tactic and still hit.
Also, this is like people asking for shadow tag chandelure. Why do you want something that would make the metagame worse by being broken?