The National Interagency Fire Center stats for fire suppression costs paint a completely different picture [1]. While the total number of fires has decreased by about 10-20% since 1985, the size of the fires in acres and the amount of money spent has skyrocketed. The annual average from 1985 to 1989 is ~2.9 million acres while from 2013-2017 the average was over twice that at ~6.7 million acres. Furthermore, inflation adjusted expenditures have increased over five fold, meaning that we're spending significantly more resources on fighting fires and yet, the number of acres on fire continues growing.
This data suggests that our houses are built with better standards, fewer people are smoking, and our appliances are safer so there are fewer fires but it's pretty clear that our problems have grown much worse overall.
[1] https://www.nifc.gov/fireInfo/fireInfo_documents/SuppCosts.p...