Covid changed a lot of attitudes around sport, businesses and people views and values around partcipation.
I think the well organised and resource rich Shute Shield clubs appeal to some players as can provide the resources that subbies cannot compete with, 'professional' training, medical and kit they receive. When they arrive at training there are 5/6 trainers, witches hats and drills set up everywhere. It is just a well organised and structured machine which comes from having plenty of bodies and money. Injuries either at training or particulary game day, are well resourced by a conga line of pyschos and ad hoc medical staff. The kit and merch, they get the flash bag, hoodies etc that makes them (and their parents, where a large source of encouragement to play "grade' and not grubby subbies comes from) feel they belong to a much larger community.
No easy answers for most underresourced subbies clubs, who despite the best endeavours struggle for volunteers and coaches, have a stretched medic on game day and can provide a training top at best along with socks and shorts on the merch front. And no I dont want to to hear about Mosman or Colleagues or Lindfield. Im talking about the reality of most clubs, not the fortune few.
The pull of grade obviously has enough appeal for a half decent player to prefer a 9.00am 4th grade kick off in front of no one in Shute Shield rather than play 1st grade to 500-1000 at 3.15pm in subbies.