Perhaps because they are not? Chase is better for some redemptions, American Express for others. You need to match the program to your requirements.
Please share the redemptions that are better for AmEx. I've looked through gift cards, flights, hotels, and items but Chase has been better so far. I have approximately 90k unused AmEx points at the moment and am struggling to find a use that's better on AmEx vs. Chase. This week, I've booked two separate hotel stays with Chase points as well as a flight. I've paid for one item on Amazon with AmEx points but the conversion was terrible. The closest that I can get to the value of Chase is getting Neiman's gift cards with AmEx points.