As PADI make money from the sale of manuals...
To be fair, I'm under the impression that's how most non-charitable dive training agencies derive a profit.
I'd assume that sales of materials and certifications would
usually be a far bigger revenue source than member subscriptions (dive pro and dive business).
The exceptions being club-based organizations like BSAC or CMAS.
Even then, not-for-profit agencies still need to expand or maintain their operations. They have an interest in promoting more training, more membership, more active divers etc.
The revenue not-for-profit organizations raise just pays operating overheads, with surplus being reinvested for expansion, improvements and special projects.
With for-profit 'business' agencies an amount of profit will always go into paying stockholder dividends or swelling private bank accounts.
I think every agency has an interest in swelling membership, what differs is the method or means by which they're prepared to attain that...and the motives that drive them.
In plain speak, it's about how low they're willing to stoop in order to maximise revenue...and how much leverage they can apply in the market to effect that ambition.