Belonging to a dive club will get you into the water more, having one connected to a dive shop usually means more door prizes for the club members and more traffic for the dive shop.
More active divers usually keep training, again more traffic for the shop.
Here at the shore the club would charter the boat which saved the members money.
If the club is not meeting at the dive shop then the dues go toward renting a meeting place but I do know some that meet at a bar but if they don’t drink then next month you need another bar!