The thing is, we're giving up something in exchange for all that savings, and it's not just money - we're giving up privacy too. You've seen it - provide your email address to get a coupon, and next thing you know, you've got three to five emails a day from that retailer. All of the stores and apps track our purchases. Ostensibly, the information can be used to make our life as a consumer easier, with personalized recommendations and deals.
But the information can be used for so much more. It can be used to create profiles about us. Like companies that know you're pregnant before you tell anyone. More broadly, it is aggregated with other consumers' info to track trends and create market analysis that can be exploited by various companies. And the data can even be sold by the companies collecting them to other companies.
There isn't necessarily anything wrong with all this. You might be just fine giving up some privacy for some savings (I often am). Or you might decide that the personalized recommendations are too creepy (as I sometimes feel). We just need to be aware of the trade off, so we can make more conscious decisions about how much privacy we want to give up for our savings.