Fine particulate matter - Why the lack of attention? What can be done to tackle it?
There has been some considerable attention, it is not that factor that is hampering more coherent action, it is a lack of full understanding of the fine particulate matter itself - allow me to explain.

A lot of the reason why there has only been largely piecemeal approaches to combat Fine Particulate Matter, globally speaking, is due to the incomplete understanding of the aerosols and their dynamics themselves.

Having said that, there are different strategies to combat fine particulate matter (FPM). But, first, a definition - the United Nations Environment Program (UNEP) page Pollutants: Particulate matter (PM) states:


  PM 2.5 refers to particles with a diameter of less than 2.5 microns. These are usually called fine particles and contain secondary aerosols, combustion particles and re-condensed organic metallic vapour, and acid components. Fine particles can reach all the way down to the alveoli in the lungs.


The inclusion of secondary aerosols, combustion particles (e.g. soot) and recondensed organo-metallic vapour can and does complicate attempts to mitigate the effects once released and would also complicate attempts to prevent the release.

It could be argued that the ultrafine fraction at 0.1 microns and less could be included under the FPM umbrella; however, as stated on the UNEP page, these are still the focus of extensive research.

There are several documents calling for the control and providing practical strategies by governmental organisations, one such document is the US EPA's Controlling 
Fine Particulate Matter 
Under the Clean Air Act: 
A Menu of Options (2006), in which it is acknowledged that


  The chemistry and physics of PM2.5 formation in the 
  atmosphere is incompletely understood. 


also, in a practical sense,


  In a perfect 
  world, control-efficiency and cost-effectiveness data would 
  be at hand; however, it is not consistently available. 


and also in a scientific - practical sense:


  there are important distinctions 
  between filterable and condensable PM2.5. Further, some 
  methods used to measure PM emissions reflect only the 
  filterable components and, to exacerbate the problem, the 
  filterable components vary depending on the test method 
  used. 


The first step in any attempts to mitigate the FPM content in the air is to monitor the sources, flow, composition etc of the particles.  From the EPA document:


  The importance of determining source apportionment 
  for ambient PM2.5 in a specific area cannot be overstated; 
  developing a cost-effective approach to controlling PM2.5
  emissions sources requires an understanding of the relative 
  contribution from local and regional sources. Adequate 
  monitoring data are needed to provide insight into the 
  composition of ambient PM2.5 in a given area. 


A British document Fine Particulate Matter 
(PM2.5) in the United 
Kingdom (2012), states the reason why action is not happening fast enough reasonably well, with


  The science underpinning the knowledge of PM2.5 is rapidly evolving and 
  remains uncertain in many areas. There is a need for rapid translation into the 
  policy arena of the newest results and understanding.


The uncertainty due to the varying compositions, which in turn affect how the particles move, how they interact with the surrounding environment suggests that 1 method would not be sufficient, and that more localised methods of control are necessary.

As you suggested, the importance of understanding FPM can not be understated, in epidemiological research Reduction in Fine Particulate Air Pollution
and Mortality
Extended Follow-up of the Harvard Six Cities Study (Laden et al. 2006), there have been found to be a drop in mortality corresponding to a drop in FPM concentrations.