Yeah, but that is the point actually: the Jews and the Christians were the only "atheists".
All of the polytheist cults were generally inclusive - if you told an Egyptian or a Celt that they need to offer incense to the image of the Emperor, they would shrug their shoulders and do it, and then go back worshipping Ubasti or Belenos as usual. It was not a theological issue - worshipping other gods beside your own main deity, or making offerings to human kings, heroes or ancestors was totally fine in most of those cultures.
Only the Jews got in trouble, because their prohibition of images and their exclusive monotheism. They had a religious issue with "idols" of the emperor being moved into their city... and the Romans took that as a political issue because their loyalty to the empire was called into question.