On a Wednesday night in late July, the Chicago Cubs played the San Diego Padres at Wrigley Field in front of an announced crowd of 30,718. Er, make that in front of 30,718 sold seats. The number of people in those seats was considerably smaller—about 19,000 by one published estimate.

The evening was unusually chilly for midsummer, and the Cubs and Padres were (and are) both well out of the playoff race, but the lagging attendance fits a pattern for the Cubs of late—one that stands in contrast to the surging crowds of the previous...