The fact is that the Buyids did not emphasize their religion whatsoever. They were happy to have the Caliph in Baghdad, and even sought marriage relations between their daughters and the Caliph (not always successful). Needless to say, the fact that they were Twelver Shi'ite played no part in their decision making. In fact they were far more interested protecting the Caliphate from the Fatimid Shi'ites (who sought to depose the Caliph), than they were in expressing their religiosity. In other words, their religion, Twelver Shi'ite Islam, was not the prime directive of their state's actions.