At least in this part of Europe, there is simply not enough space at most gas stations for any significant proportion of vehicles to spend more than five minutes there.
My experience is that roadside parking outside residential property is in pretty short supply across much of Europe too.
Right now there are two types of people that go to those stations.
1. People there to put gas in their car, and
2. People there specifically to visit the convenience store.
Gas stations tend to be in places that won't get a lot of foot traffic, so what is going to mostly determine how many potential customers they see a day is how many cars they can accommodate at once and how long those cars stay.
Group #2, the people specifically there for the convenience store, are both very likely to buy something and not likely to stay long.
Group #1, the people there for gas, may or may not also buy something from the convenience store. If they do, great. If they don't at least they won't stay long because gas powered cars "charge" fast. A reasonably well maintained gas pump is over an order of magnitude faster than EV chargers.
If they add EV charging the EV charging area will probably have to either take space from the gas pumps or to take space from the place group #2 parks.
If they take the space from group #2 parking, they are replacing people highly likely to buy with people less likely to buy and more likely to stay around longer. It is hard to see how this could ever be a win for the store.
If they take the space from the gas pumps then they are replacing fast gas fill ups with slow EV fill ups, which cuts down the number of potential convenience store customers. Maybe EV drivers will be more likely to decide to buy something in that extra time, but I suspect that won't be a big effect. I'd bet people who buy from the convenience store just because they are killing time waiting for EV charging will mostly just make small purchases.
On the other hand, it really is #2 that provides most of the profit. It is possible that group #1 is a sufficiently small contribution that it doesn't matter if replacing some gas pumps with EV charges lowers convenience store sales.
Sometimes I think selling gas at those stores is mostly for awareness. I'd guess that a lot of the people in group #2 are only there because at some earlier time they were in group #1 there. They decide on Friday or Saturday night that they need to get some beer or cigarettes or lottery tickets and remember, and because they got gas there earlier that week they think of the convenience store.
Putting in a couple EV chargers in place of a couple gas pumps might turn some EV drivers into group #2 people who otherwise might have forgotten about the convenience store.