It's a vicious cycle thing, if Beltran had been a better sport then the writers and producers would have tried more with him. By being a dick, he just ensured they wouldn't give him more chances in the future.
Of course, there were fundamental problems with him to begin with. Being a former Fleeter who had no problems with the Feds (otherwise he'd have outright defected and betrayed secrets instead of formally resigning) doesn't make for a good foil to Janeway.
Of course, there were fundamental problems with him to begin with. Being a former Fleeter who had no problems with the Feds (otherwise he'd have outright defected and betrayed secrets instead of formally resigning) doesn't make for a good foil to Janeway.