As I understand it play has to stop when a doctor comes on. That’s when the green card comes into play. If it’s just a trainer that comes on play doesn’t have to stop. Hope this is right.

Probably can't be bothered. They struggle to get yellow and red cards oitbtheor pockets.
Need bigger pockets or smaller cards

Newman got one v London the other week, went down like he broke his ankle, physio raced on, didnt see the doctor come on, at the time of play there was about 2/3 minutes left and London were on the Leeds line after a break, call me synical, but it was blatentley a proffesional foul imo and a feigned injury, he was issued a green card, stopped the game which meant Leeds could regroup and takeaway Londons quick attack and overlap if the game was allowed to continue like most other games would have, 2 minutes later Newman was back on!

5 – Green Card
The Green Card will continue to be used in the circumstances described below, but only in the Betfred Super League (no longer in the Betfred Championship), and only to be shown to players on the defending team (it can no longer be shown to the ball-carrier).
It was introduced to reduce the time taken to deal with injured players on the field of play, without compromising player safety – so if the referee has been requested by a physio or doctor to stop play because of a potentially serious injury to a defending player, and the player involved is not interchanged or taken off for a Head Injury Assessment (HIA), the player will be shown a Green Card requiring him to leave the field for two minutes of elapsed playing time.
Also as previously, a Club may use one of their interchanges to allow the player to remain on the pitch.

With the number of ball carriers feigning injury it needs to be extended to both sides. Also, if someone goes down holding their head they should automatically come off for a hia in my opinion