In the end tho, its us, the people, when we first make a airline rev booking, or when we buy our groceries, from Coles/Woolworths.
Airlines are not dumb/stupid, they know how to make money.
When we pay for an item at some places, they will say, "oh, there is a credit card surcharge", can be up to 0.0015%, but on a $10 meal, its $0.17 to the bank.
Then when our data gets moved between partners, airlines/hotels/etc, they are worth something too, your email address can get onsold, to a survey company for the hotel to send you a "survey" form, and you have the "option" to fill it in, or not, but they can pester the bum out of you, to fill it in.
If we made a booking with Airbnb, we also pay, for it then, ...
You have to spend to get the "points".
I know someone who doesn't do these rewards things at all, tho.
Look at QTMC/the former Qantas Cash card.
They don't pay us interest, no matter if you have a large sum sitting in it, for an upcoming overseas trip, but for those of us who do not want real debt, or can't get a "real" credit card, this is the only way to earn QFF points on a regular basis.