Do people really go comparison shop between stores? Like, I recognize that I'm coming from a more privileged economic position to not do so, but I still go to the cheap grocery store because it's the closest to me.

I'd imagine that even for low-income people, it's the cost/benefit of comparison shopping has been squeezed out by how much prices change on a day-to-day basis. Like sure, if you're buying a lot of something all at once it might make sense to do on that occasion, but once you do that a few times you either learn:

1. Which store usually has the lowest price (and if they have coupons for store X, they might just only go there, because... they can't use the coupon at the competitor's)

2. The difference in price doesn't offset the time-cost of going to multiple stores (and the consolidation of stores means that going to two different stores will take even more travel time).

So, if most people aren't really doing comparison shopping anyway, then you make more money by matching your prices to your competition.