I’m pretty sure the loyalty-card thing has become so big because they’re selling the data.

So many things are like that now. Like Roku sticks and TVs are subsidized by selling user data. You want to make a Roku competitor that doesn’t spy? Your product will struggle to get on shelves and to stay there, in part because the price for your product will be higher even if you get just as good a price on your components as they do, because you’d have to price them at-cost to match Roku’s pricing. Meanwhile 99% of people looking at the products don’t realize that one’s cheaper than the other because it’s going to spy on them and sell the data.