Boston and LA were also the only two franchises in the league with any real history too (league was barely over 30 years old when those two got drafted). The Bulls had no history whatsoever before MJ and yeah, that changed the direction of NBA marketing.
If it happens with the NBA, it probably will take another 30 years or so like another poster said. The league itself is still really young in the national eye as far as popularity.
I can understand why you said Boston and LA are the only real NBA history but I remember I watched Bird vs Magic documentary. Magic was talking about how he was so shocked that black people from Boston are rooting for Lakers. Magic was like
You rooting for us against your own city?...why would you do that?. These black fans from Boston were like
"fukk the Celtics, I don't root for no damn white folks. Gotta support for my black people like you, Magic"