The article covers this.

> In the 1990s, a wave of lawsuits holding architects and engineers liable for health problems related to poorly built or maintained buildings led to massive overhauls of construction codes. The new codes created restrictions for the materials architects and engineers could use in buildings and HVAC systems. “Buildings were afraid of litigation,” said Sachin Anand, an engineer who leads a Chicago-based sustainable building firm. So most of them made meaningful changes that ultimately led to much healthier indoor climates all over the US.

> By the early 2000s, complaints of sick building syndrome — and concerns about indoor air quality more broadly — had faded from the public eye.