The mainstream media has moved on, because they already made their point - gun control, and that is the only narrative they assigned, wanted to assign or will assign to the Las Vega disaster. They have no desire to destroy their own narrative with any investigation that could produce facts contrary to that narrative. That charade by the media is no mystery.
I knew after the shooting in Orlando, where there was no denying the Islamic motive, and we see what happened. It is mostly ignored except to bring up gun control, and the Jihadist motivation is blatantly ignored.
A squad of Jihadists could illegally enter the country and bring their guns with them. They could commit an atrocity, be caught and tried and talk constantly about their motivation, and all the media would talk about is making it illegal for law-abiding citizens to have guns.