It is typically much cheaper to retain a customer than to acquire a new one.

That said, the whole idea of targeted marketing campaigns is to change future behavior of specific current customers or future prospects. By targeting the campaign, the cost is much lower than if the offer is made to the general populace.

In an Acquisition campaign, the company looks for prospects with high potential profitibility. In an Expansion campaign, they look for existing customers who may give the company a bigger slice of their business. Retention campaigns are (sadly) probably the least common, and tend to target customers with high perceived risk of erosion (less business) or attrition (leaving altogether).

The point is, if you have been giving the company a lot of your business, at a steady level, for years and years, unless you fall in some odd demographic bucket, you are perceived as "not at risk" and are not likely to attract any high value/cost offers.

Is this a lack of Loyalty? It's not about Loyalty, it's about profitibility. And that's a two way street. If another card came along with all the same benefits, but triple miles always, most of us would switch in a second, no matter how well Amex had treated us in the past.