He hasn't earned a shot at back row ... he has earned his wing position, but not back row.
If he wan't to be a backrower, then he needs to learn the position and you don't do that at NRL level. and just in case you were wondering, backrow and wing are completely different positions. different work loads, different defensive structures, different attacking patterns and plays etc.
playing a few minutes in trials against weakened opposition doesn't in the slightest prepare you for playing top level opposition.
at NRL you don't have time to wait and hope that a player picks up a new position (especially the defensive differences), it is far too risky to allow him to get found out then have to play catch-up for the remainder of the game ... if you need to do that in too many games, you can kiss goodbye to the season.
Now Oates may leave thinking he will get a crack at playing backrow at another club, without first learning the position in the lower grades, but he needs to be very wary ... he only needs to look at the players to have left the club because they were promised a certain position, only for their new clubs to "change their minds" once they have them signed.