It’s behavioral intention vs. satisfaction. Another reason for why the NPS correlations with growth were nominally higher is because the NPS is a measure of behavioral intention (likelihood to recommend). In contrast, the ACSI is a measure of attitude. While attitudes do predict behavior, they tend to predict behavior through behavioral intentions. This idea is also supported by Pollack & Alexandrov (2013), who argue that satisfaction can be seen as an antecedent to repurchase intentions.