A myth. The episode with Locarno was by staff writers, wouldn't have needed any extra fee to re-use the same character. Ro was already semi-regular character too, same deal.
I think Ron Moore, one of the staff writers for that season of TNG, mentioned this in a recent interview.
In interviews the producers of Voyager have said they felt Locarno's actions in that episode made him "irredeemable". (TNG Season 5 DVD-special feature, Memorable Missions Year Five: "The First Duty")
Ask the writers. (I guess they didn't want actual blood on Paris' hands, or decided it didn't make sense for him to be back in the fleet, which is what Lower Decks have done with Locarno)
According to Robert Duncan McNeal, Larcarno gave the impression of being a good guy who made a mistake when in reality deep down he was a bad guy, whereas Paris was the other way around.