Well, you can always pick and choose your examples, but the author is on the right track. Popular music is the same as it was 20 years ago, just with different acts. Movies are dominated by the same “blockbuster adventure” mode started by Jaws.
My take on the cause: cost. The price of everything has gone up. Movie ticket prices have far outpaced inflation (from an average price of $4.15 in 1992 to an average of $7.89 in 2010). The same for prices across the board on most other types of art.
The one exception is music, where you can download an album for less than a CD at the time, but the cost of an album of music on iTunes is far more expensive than file sharing, so the low price still looks high.
The result is that, as people pay more for their art, they stick to the tried-and-true. For $4.15 in 1992 (the equivalent of $6.37 today), you might take a chance on a film, but when it’s an extra dollar and a half* (plus inflation on the cost of popcorn, drinks, and gas), you don’t want to take a chance.
While there are niche performers, there are far fewer than in the 90s, they are much harder to find (even with the Internet), and fewer of them have a chance to make any money at it.
I saw the issue occur on Broadway 30 years ago. Back in the 50s, a play could have mixed reviews and still limp along, as people would give it a shot. But as ticket prices rose, it became either smash or flop, with nothing in between.
At the same time, as the cost of making art increases, then you become wedded to the blockbuster mode. When you’re investing hundreds of millions of dollars in a film, you don’t want to take any risks. So you go with genres that are sure things (there’s also the fact that even flop action films do well overseas).
Ultimately, the more you have to pay to see a movie, or go to a concert, or see a show, the less likely you are to take a chance. Thus people stick with what they know, and those who are outside the mainstream have a hard time breaking through.
*Also, people judge the cost of art as an absolute number. Even though $16 for a hardcover book in 1993 was not considered an unreasonable price, $25 for one today seems expensive, even though inflation makes the two amounts equivalent.