A lot of these go hand and hand....
At the end of the day some guys just have IT and some guys don't.
Tank has been the man since he came on the scene. Part of it is Mayweather pushing him so you have someone who was the face of boxing leveraging his fan base but also Tank is delivering exciting fights and knocking everyone out.
The thing you notice about Mayweather fights is that he brought the African American audience out to Vegas for his fights. People will fly and spend money to be apart of his weekends........Tank is the same whether he's fighting in NYC, LA or Vegas. I saw Allen Iverson shut down an entire sportsbook so that him and his friends could watch him fight Hugo Ruiz.
What's really missing from this list is that you need a style (exciting fights) or a personality which allows you to transcend boxing and hardcore boxing fan and capture the general public. Adrian Broner had all of the qualities of being the star but he couldn't deliver in the ring. Tank delivers in the ring, Spence delivers in the ring. Haney and Shakur are boring despite how great they are and they don't sell themselves in a manner that casuals will catch on. Crawford left himself stuck in Top Rank purgatory.
Keep in mind that casual buzz also means celebrity buzz and we all know that in America, that celebrity is king. I'd argue that most boxing fans these days are casual fans who like the big fights.........and people would be more invested if boxers fought as often if they used to and the top guys actually fought each other.