A top goal of Vince McMahon and WWE management recently has been to make Randy Orton more of a main event priority. This stems from Orton approaching company officials last month, unhappy with his booking, and requesting time off.
The original plan for Hell in a Cell was for Orton to co-headline the show against Roman Reigns. Once Reigns was pulled due to injury, it was clear in speaking with sources that WWE planned to cater to Orton in order to convince him to stay on. Vince realizes the top of the card is devoid of overall star power and doesn't want Randy to take time off right now.
Orton wasn't thrilled with the idea of getting the LOSER of John Cena vs. Dean Ambrose at Hell in a Cell, which is probably why they moved the match up to Raw and have now added the title shot stipulation.
Vince did recently approach Orton about regularly working Smackdown on Tuesdays, but Orton declined.