Sure, the real reason most people didn't stop is that in a world of crowds and tight schedules, people are too focused on their own lives to notice the world around them. In large crowds of strangers, the only way to get from point A to point B is to ignore everyone else, so you don't have to get involved in anything unexpected. If he had been in the middle of a mall, where there's always someone just killing time, there would have been an instant crowd.
However, the reason more of those who actually pay $1000 to go to concerts and listen to world-renoun classical musicians perform didn't stop and notice was that they only ever went to any concert to flatter their own idea of themselves as an individual of high tastes, much as the article writer probably does.
And that's why, with all the people rushing by, they didn't even get a small crowd. It's shocking to those who believe people actually have taste, but for those of us who see right through the image game, it's about what we'd expect.