This is starting to get boring now, you have an alternative theory but have not said why.
As Parra were given cap dispensation for a new injury to Watmough, Manly were hoping for the same with Matai and Stewart and bought players accordingly. They were denied as were existing injuries. They also continued buying players close to season start including Perrett from Dogs and Hastings, both who are probably costing them $200k each with old clubs paying difference. I mention $200k as no good clubs releasing players for less as they come out of top 25 while the next lowest player comes in at min $85k.
As I said DCE on $1m plus 2 turbo, Walker, Green and Taupau each on $400k (this is a low figure imo) making $3.0m with Matai and Stewart at $1.5 with cap of $7.5 so $3.0m left over for 17 players or $176k each. See how hard it is to fit everybody under cap and why my suspicions are raised.