While we can't say why Apple is having a a last minute sale, but they are right now on Apple's US Home Page as you can see in our cover graphic. The offer is not available in Canada at the moment.
Moments ago the home page began with the announcement of the iPhone XR from $449 with a trade in as noted below. Apple doesn't spell out the particular iPhone versions or the exact trade ins when you click on their offer so it's a little difficult to figure out what Apple is doing other than trying to get rid of inventory.
Earlier today Apple launched a special iPhone deal for U.S. Veterans and Military Purchase Plan.