I see both perspectives here, and while I think the actual impact on crowding will be trivial (consider how restrictive AMEX has become in the US which has so far had marginal impact on AMEX and Delta lounge crowding), some will see more upside to the changes and others more downsides.
Ultimately the strategy is pretty clear: Qantas wants you personally to have a credit card, pay for one-off access, or chase status --- preferably some combination thereof, especially as they move towards status-earning possibilities on the ground with said credit card.
Restricting lounge pass transfers to pax travelling on the same flight cleverly renders them useless to anyone with SG/WP in most cases. Literally can't even give them away for free. In practice, that means your everyday punters now need their own credit card or to pay for access. No more free-loading = opportunity to upsell / generate revenue.
Ultimately, the motivation for the change and the winner is Qantas. That's always been the game, though in my view, sometimes it's better to simply state the new policy than try to come up with silly justifications for it (e.g., "we need to stop unauthorised transfers", "reduce crowding", "protect FIFO workers having pints and corporate bros on their Zoom calls from the uncivilised riff-raff," etc.).