Because it's faster in the long run.

If you are going to type a message, you are already resigned to placing two hands on the keyboard. If that's so, you might as well learn the keyboard commands involved with sending messages in different ways.

Most people know the /me command for sending actions; no dialog needed. It is learned once and memorized through repetition. I suggested above the creation of the alias /a as a shortcut to /scon -a that should be similarly easy to remember especially through repetitious use.

/a ame is king of the world! -- Send to all servers, to all channels, who is king.