The number one priority would be advertising revenue. The sales team is always under pressure to ensure the local news is fully subscribed - and to do this, they need it to be distinct and recognisable.
For example, Jenny the sales rep in Wagga might go in to Joe the butcher on, say, Baylis St and ask him to sign a new ad package. Joe will say, "Is Channel 2 the one with the sheila reading the news or the one with the bloke and the sheila? We like the one with the bloke and the sheila."
Jenny can say, "oh yes, we have two news readers now on Prime 7 - we haven't been RVN-2 for a while - but I know what you mean, it's confusing how we keep changing our name and number!"
Job done - they can provide a news service that is distinct and different to WIN and Nine, simply by adding a presenter.