He was assassinated because he was not doing his job and/or he was incompetent at it. It wasn’t a tough sell.
Disagree...he was killed because he was an excessive pervert who offended the normal pervs.
The ancient sources record many of Elagabalus’ other misdeeds, though they are too many to recount here. It is clear, however, that the emperor’s eccentric behavior alienated him from the rest of Rome. Ultimately, in 222 AD, the soldiers of the Praetorian Guard decided to remove the emperor themselves.
Herodian reports that the soldiers were in favor of Elagabalus’ cousin, Alexander, since he seemed to be a more suitable person for the role of emperor, and, more importantly, because of the gold secretly distributed to them by Julia Mamaea. Elagabalus soon learned about this, and plotted to kill Alexander, but his plots were foiled by Julia Maesa. Both Cassius Dio and Herodian record that Elagabalus was ultimately murdered by the Praetorians when he was in their camp. The emperor had gone there with Alexander to try to calm the soldiers, who were angry when they heard what he was trying to do to his cousin. Elagabalus failed in his task, and was executed in the camp, along with his mother, and several of his close collaborators.
The narrative of Elagabalus’ death in the Historia Augusta, unlike the two other sources, focuses on its irony, and is as follows,
“The prophecy had been made to him by some Syrian priests But all these preparations availed him nothing, for, as we have said, he was slain by common soldiers.”
Finally, Elagabalus’ corpse was dragged throughout the city to be publicly abused and mutilated, before being thrown into the public sewer that flowed into the Tiber. Thus, the story of Elagabalus, one of Rome’s least favorite emperors, came to an undignified but just end