Anecdotally, I agree with your assessment that EVs will cause more purchases.
The point of those stores is to get in and get out quickly. It's the exact opposite of an EV charging station. In fact, most 7/11 in my area enforce the 'no loitering' rule.
I don't even think that 7/11 managers want you there for more than 5 minutes.
Restaurants or shopping malls I'll stay for 2 hours regularly, and a few level 2 chargers can actually get me 50 miles of charge in that time. That's where the EV chargers should be.
I’ve traveled through most of the western (ie west of the Rockies) United States and North east as well. It’s possible I’ve seen a 7-11 gas station and just don’t remember.
Dunkin doughnuts vs Starbucks, Hardee’s vs Carl’s Jr., etc.
In the Seattle area, it looks like 33/100 of the 7-11s have gas. For LA, it was 1/100. For Toledo Ohio, 1/10. For Dallas Texas, 50/100 it looks like.