I think that the gradual elimination of constant fog effects has to do more with liability issues and illnesses. There have been multiple outbreaks through the years and it's becoming an even dicier predicament with recently rare diseases making their reappearance. The following article references an incident we had in Nashville several years ago:
"Mist infects 100 in a Rainforest Cafe
Bacteria in a theme restaurant's rain forest simulation is to blame for an illness that struck about 100 diners in Nashville, Tenn., the
Centers for Disease Control and Prevention confirmed this week.
Customers at the Rainforest Cafe in the Opry Mills shopping mall came down with Pontiac fever, a mild form of flulike Legionnaire's disease, after they visited the restaurant the weekend of April 19, medical officials said.
The contaminated mister has been turned off while the state health department develops a plan to clean it. The agency will begin routinely testing it for safety when operation resumes.
Houston-based Landry's Restaurants, owner of the cafe, plans to reimburse the cost of meals to affected patrons."