Hello,
The league you are currently in only has 6 managers in Rookie. To activate promotion, the tier must be half-filled (8 in a 2 car league and 16 in a 1 car league).
If you are struggling to attract Rookies to your league, I recommend advertising your league in the
Leagues and Events subforum or inviting your family and friends in real life to join your league.
If you still aren't getting enough Rookies to activate promotion, you could make a few extra, new 'Place Holder' accounts to boost your Rookie tier numbers. This could also lift your tier to 14 managers, which is the ideal number for your league to be advertised on the filters for when new players join the game.