Derek Carr is really weird. He's had excellent production now for 3 years straight. If he throws for 270 today, he'll go over 4000 for the 3rd straight season, while increasing his air yards, QB rating, yards per completion, and TDs, while lowering his INTs in each year. Yet, he hasn't had a winning season since 2016 and that was the only year he's done that.
But we've seen good QBs who couldn't win consistently before. Stafford in Detroit, Rivers in San Diego, Ryan in Atlanta. He's only turning 30 this year, so he's not old for a QB. It would be a very bold move for the Raiders to get rid of the few really good QBs in this league. But if they don't think he can be more than a good QB, and can't get them to the next level, it's a very understandable move to trade him. But be careful what you wish for.