Deportation hearings aren't to determine the legality of your presence (That's already been established, hence the hearing to decide whether you should be deported). So the "criminal" part is already decided, deportation hearings are administrative and AFAIK court appointed representation is not required for administrative hearings
Deportation isn't a punishment for entering the country illegally. Deportation is the administrative removal of a person who doesn't have a right to be here.
An analogous example is trespass. A landowner can call the police to kick you off his property. That's not a criminal proceeding. But then the state might then prosecute you for criminal trespass, punishing you by depriving you of liberty (jailing) or property (fines). That is a criminal proceeding.