1980 was a different time. The NFL and the NBA certainly weren't anywhere near as popular as they are today and they weren't the marketing moguls they are today. I mean, Vince Ferragamo chose the CFL in 81 over the NFL because he got offered way more money. Baseball was America's past time. The options for kids entertainment in 1980 was completely different. Video games were for the rich and pong was the pinnacle of gaming! No internet, no computers. Baseball was way more accessible to kids in 1980 because so many kids played. It was far cheaper. 40 years later there's way more choice for kids entertainment hours at very affordable rates. Less kids play sports in general and a lot less kids play ball. This drives the costs up.
I don't really think "the black" viewership is important. I don't like defining people by the colour of their skin. We need to look at low income, middle income and high income earners and their participation in TV watching and in game attendance. The reality is ticket prices have driven the low income earnings out of stadiums. The romance has been lost. In 1980 going to a baseball game was a very reasonable priced family outing compared to going to the movies and other forms of entertainment. Black people statistically as a proportion of total population have far more low income earners. Baseball has lost this group because of rising choice of low cost entertainment options outside the sporting world, as well as increased competition within the sporting world and the rising costs in baseball have priced out some of this segment to some degree.