A source tells ET that the 35-year-old decided not to attend simply because the event was on too grand of a scale -- as he likes to remain low-key.
“Rob knew Kourtney and Travis' wedding would be a big affair with cameras and paparazzi, so he decided not to go,” the source says. “He likes to stay out of the limelight and feels more comfortable attending more private family events and parties where he can be more under the radar.”
Although he was not there, Rob still offered his support to his big sister and her husband. “He's very happy for Kourtney and supportive of her,” the source adds. “They are still very close and Kourtney understood Rob's feelings, as did the rest of the family. Rob is continuing to focus on being the best dad to Dream and absolutely loves being a father."