You sure? Walmart already often has Electric America charging stations installed and those regularly see a lot of use. Lines aren't uncommon.
Not to mention, having chargers at your store means you have customers charging their car which can take at least 20 minutes, usually more. Customers that may decide to do something while killing time....like shop at the store you're already in the parking lot of.
I primarily charge at home, but on road trips I primarily use Electrify America due to being on a free charging plan, and since these are very frequently at Walmarts, I visit Walmart quite often as a result on these trips, where I would almost never step foot in one otherwise.
Speaking of such, rural areas are a great spot for these. I, like many, charge at home. It's way cheaper than using a fast charger (unless you're on a free plan, of course). Where we need fast chargers? Places where we don't live. And believe it or not, people often road trip to or through rural areas.