I've said all I need to say, laid out the bones and signposts. The reader already knows where I'm going in the rest of the piece. This would be a good place to stop, then, no? Why fill up another page with expository throat clearing? Why not just dive right into the meat of the piece?
Because the editor views it as skimpy. Be complete and precise, even if it means loading up the opening with a bunch of stuff that everyone is going to skip over.
You know what? Screw it.
If it bores me to write it, then what are the odds that anyone is going to read it?
"She slipped the gun back into his holster. Now that the last four rounds in the clip were blanks, the cop wouldn't kill the kid in the firefight this afternoon, and Earth would be united when the invasion came, 120 years hence."
I'm not going to tell the audience much anymore. Let them work for understanding. Screw it.