Somehow the Nephites also became idolatrous in some way. Idolatry is defined in the Law of Moses at the beginning of the Ten Commandments, in Exodus 20:4, "Thou shalt not make unto thee any graven image or any likeness of anything that is in heaven above or that is in the earth beneath, or that is in the water underneath the earth. Thou shalt not bow down thyself to them nor serve them." Abinadi quoted the Ten Commandments to the priests.
What behaviors constitute committing idolatry? This legal subject always raised debatable questions in Jewish law. Is it okay to make a statue of a fish just for decoration, to put on your mantelpiece? Is it acceptable to make a tree, to carve a nice wood tree? Is it the making of the image that is problematic, or was it the worshipping of such images, bowing down and serving them? How far can a person go before he or she has committed the offense of idolatry which was punishable by death? My guess is that Noah had commissioned the making of many statues or stelas, likely including images of himself or of other people or things, and that he quite likely worshipped those images in his heart. He was probably smart enough not to actually bow down publicly in front of them or to put sacrifices at their feet, but there are plenty of traditions within Judaism that say making a statue, in and of itself, is idolatry, and that the other elements of worshiping those images were separate additional offenses.
In ancient Israelite archaeology, one does not find many elaborate statues like the ancient Greeks and Romans made, but some early Israelites actually did make and use small statues. But statues of human images were prohibited by orthodox Jews. Clearly, whatever their conduct in this regard, Abinadi believed that Noah and his priests had gone too far. Noah may have employed so many priests because his propensity was to get as close to the line as possible, and so he needed many advisors to rationalize his behavior.