Stafford was with the Lions with 12 years where they were nothing much more than stumblebums. He's nearing the end of his career (most likely); and the Lions were just starting ANOTHER rebuild from scratch.
Can you see the reasoning in asking for a trade?
Goff has recovered perceptions of him from leaving the Rams with a bad taste in a lot of peoples' mouths, whether that was his fault or not. This Lions team looks like it's on the upswing and could become a dangerous playoff/ SB contender for the next 5-ish years +/-, and Goff is a huge part of that. Regardless of whatever other QB moves they make BEHIND him.
Quit telling us what YOU would do. Goff is looking at making a run to the playoffs with the Lions. And trusts Holmes/ Campbell implicitly (I don't know that, but I believe he has intimated that and they've been heavily pro-Goff-Positive in ALL of their public communications about him...). What would HE do, regardless of how they BACKFILL the backup QB spot(s)?