People often conflate loyalty and incentive programs.

A loyalty program aims to keep me buying products I have to buy at one place rather than multiple. Buy that ticket on AA instead of DL.

A incentive program aims to get me to buy something else/extra/more. Buy that donut with the free cup of coffee at Dunkin.

An loyalty program can have elements of an incentive program (and the other way around), but it's the primary purpose which is key.

AA offers me many elite benefits (MCE, Priority Boarding, Lounge Access, elite call lines during IRROPs, etc) that make the trips I am already going to purchase better, and therefore induces me to purchase those trips on AA; rather than UA or DL where I don't have those benefits. Loyalty. It doesn't cause me to buy an extra trip so I can upgrade it with miles. Incentive.