#2. No other match available
The simple fact of the matter is that there's really no other option for AJ Styles and Randy Orton this year. Could they have inserted them in a mid-card title match or any other throwaway match? Sure.
But the two are bonafide top stars in SmackDown and all of WWE, and with no other plans for them and several marquee matches stacking the card, this is the best option for both of them.
On the SmackDown side of the card, it's looking quite stacked, with Shane McMahon vs The Miz, Daniel Bryan vs Kofi Kingston (potentially), Styles vs Orton, and The Usos presumably in a multi-man title match while Asuka will likely have an interesting opponent too.
It's crazy to think that they likely won't even be close to the main event. Don't be surprised if this match goes on second or even third on the card. It's just that stacked!