PWInsider.com is reporting that WWE made the decision to book the 10 man tag team match at Survivor Series at the last minute, as the company originally planned to book Rey Mysterio vs Alberto Del Rio in a 2 out of 3 falls match instead. This is why WWE's website erroneously posted a banner ad featuring Mysterio vs Del Rio.
Mysterio has been dealing with an inner ear injury as of late which is why WWE made the call to scrap the 2 out of 3 falls bout. Company officials figured it would be easier on Rey if he were involved in a large tag match as opposed to a singles match so that he wouldn't have to work as much. Mysterio has been used sparingly on TV as well as he battles through this current injury.