How is it that a big spender isn't profitable for Amex? The cost of points/rewards/cashback comes out of the revenue/profit. Who is it they want?
Because the cost of points is, at best, only slightly lower than revenue. A lot of the time it is higher.
For example, the biggest retailers in Austalia have considerable sway over Amex so the likes of Coles, Woolworths, Bunnings only pay about .5% in merchant fees. On a platinum card, earning 2.25 points per dollar, the cost of points alone is about 1.1% (depending how they get redeemed). Then there is the cost of advancing the funds for a month.
Or take Sniip; if you are paying Sniip 1.5% (including GST), then the amount Amex is charging Sniip is going to be closer to 1.1 or 1.2%. Again, not profitable spend.
Most small merchants get sweetheart rates, too. And what's left over the rate is probably about 1.5%.
The most profitable customers are those that are spending at ATO (as there are fewer reward points) or some higher discount rate merchants (there are still some that exist in the travel space, for instance). Also those that make use of the few other sources of revenue (such as booking through Amex Travel).
Business spend tends to be more profitable, as the rate for Payment Logic etc is higher. However, there is concern that regulators will not be happy if Amex knowingly allows lots of business spend through a personal card, hence the push to get people switched over to a business card. The business cards also can charge interest for revolving (which consumer charge can't do).
So who are the profitable customers? Credit cards (only if they revolve and generate interest revenue), Platinum who spend either a lot on travel/dining OR business spend OR don't use all the coupons/lounge access.