I think the idea is that you want to showcase black love to the most people who can receive.
think about it like this. you have a black young man who does great things for his community but it never goes beyond that. now that another young black man who kills someone and this is reported on the national news outlets. you have two people who did two different things but because one had a larger audience the perception and biases surrounding that individual can impact how these people see others who look like him.
the same is true for black love, having a popular couple be representative if this allows for a greater visibility to thos and it reinforces the idea that black love is beautiful.