I am a happy customer of both a bank and a grocery store. If one day the grocery store decides to also open a bank, I won't suddenly move my accounts there just because I go to the grocery store every week. That's why the grocery stores trying to offer credit cards usually have some loyalty programs (e.g. points/discounts for in-store purchases). And BTW, they typically just partner with existing banks and not try to butt into a heavily regulated market with no previous experience.

And if I never needed to have a bank account before, just being able to open it while paying for my food won't suddenly create the need for it.

You are not the target customer.

Grocery store handle a surprisingly large amount of money transfers and act as pseudo-banks to many of the unbanked. Some of them have their own banks on top and others have bank branches in them. Lots of people use these services.

Interestingly the grocery store bank thing more or less happened in Ontario and it’s quite good/popular: https://www.pcfinancial.ca/en

I am actually a happy user of this one (Vancouver, BC), but solely because the effective discount you get for using their card in the store is considerably higher than my regular card gives (there's a complicated system of points that add up nicely). And, yep, I still use my regular Visa Infinite for all other purchases because you can't beat their insurance and cashback rate.

Tesco, one of the largest supermarket chains in the world, also has a bank: https://www.tescobank.com/

In the U.S. it is quite common for grocery stores to have a small bank branch inside them for exactly the reason you cite.

> they typically just partner with existing banks

Grocery stores or Walmart?

Grocery stores often have a branch of an existing bank inside them, but the ones that don't often provide some financial services like cashing checks.

Wal-marts cash checks, do money transfers, and provide debit cards which act as a pseudo-bank account since they can be used with direct deposit etc.

That’s not an apples to apples comparison. A grocery store doesn’t have a network effect, Facebook does. That’s a powerful thing when we’re talking about products that exchange value with other parties in the network.