Religion is a social construct wherein humans organize and participate in communal activities for the purposes of creating human connection/bonding and quelling anxieties through relinquishing perspective of control in life.

Trying to make an AI preacher is an exercise in trying to emulate the latter without the former. The latter is spiritualism: the beliefs a person creates/adopts to create a sense of 'belonging' in the world. The former is the aspect that takes spiritualism and turns it into religion, as religion is essentially the social commodification of spiritualism. Of course no one seeking religion is going to be satisfied with an AI preacher, because anyone seeking religion is seeking human connection. You could use an AI to discuss spiritual beliefs with people instead, but at that point you're not creating a preacher, but rather a chat-bot theologian.