Why do you describe it as a "scam"? It's all out in the open. Every participant is a willing participant. No-one is forced or tricked into it.
I got an Amex Blue credit card in July 2001. Since then, I've spent about £100,000 on it (I use ot for everything I can*), and had about £1,000 of that back annually, by credit against the July bill (starting in 2002, of course).
Is there a downside to this?
[* At first, a significant retailers wouldn't take it and I needed to retain my bank-isued Mastercard as a backup. But this has changed; now, only a very few retailers won't accept Amex.]
Let them get and use a credit card. There's nowt to stop them.
That's nonsense. Any business has customers who are more "profitable" and customers who are less "profitable". It's never been any different in any line of trading.