First thing that popped up: https://www.businessinsider.com/credit-cards-sell-purchase-d...
So, we know they sell anonymized data. We don't know if its easily de-anonymizable because that takes some studying, and we don't know what else they are selling they don't tell you about.
It's not that I prefer cash, it's that I don't see involving 100s or even 1000s of third parties in all of my transactions as an 'improvement'.