1) this is false. $1mm credit card spend means a bit over $10k in revenue for mileage sale with most programs
2) the revenue to the mileage program is much, much higher independent of the revenue to the airline
3) the cost to the carrier is much, much lower
4) with high load factors, losing one paying passenger just means incrementally less revenue than the spend of that passenger, since the airline would sell most of the seats to someone else though perhaps at a slightly lower price. whereas with mileage sale the revenue is all at the margin.