I vaguely recall reading a few articles about how firehouses are less necessary as we have less fires today, but we struggle to reduce their numbers as they are heavily unionized. This is the narrative I at least have floating in my mind.
This is a UK perspective but IMO much of the reduction in fires has been because of the work done by the Fire Brigade. Education, information campaigns, pushing for reforms, calls to action etc. Any reduction in numbers – and the manner in which it happens (in case it has a multiplying effect of disuasing new recruits when they're actually needed) – should be done very, very carefully.