Weird case. They advertise enough on Black media to get the customers they want. Then they advertise on non-Black media to get more customers (who also may be Black). No point in oversaturating Black media with McDonald’s ads when they’ve achieved their goal.
You make an assumption that the purpose of advertising is to create customers.
At one time that was true but I don’t think so anymore based on observations.
The current purpose of too many companies is wokeness.