Well they believe in doing the opposite of what prophet(Saw) taught to muslims..So they just attributed the opposite practise to ttheir imams. There are narrations that hz ali(ra) too used to offer salah like the ahlesunnah, as well as from the prophet(Saw). 2. Because they are grave worshippers. Did ever hz ali(ra) or hz hussain(ra) used the sand from the grave of prophet(Saw) for doing sajdah on it? If no then why? Didn't they consider prophet(Saw) the best of creature? And if they didnt do this then it means that they diodnt consider this to be correct. BUt the rafidah are known for innovations unislamic things in islam.