Why is smoke considered a factor of global cooling when analyzing nuclear winter scenarios, but arent when analyzing global warming scenarios? In many articles on the internet (I'll cite a couple for the sake of the question), smoke from the fires (composed mainly of $\small\mathsf{CO_2}$ and CO) following a nuclear war would cool the atmosphere and would cause a "nuclear winter". 


  Nuclear winter is a severe and prolonged global climatic cooling
  effect hypothesized1 to occur after widespread firestorms
  following a nuclear war.[3] The hypothesis is based on the fact that
  such fires can inject soot into the stratosphere, where it can block
  some direct sunlight from reaching the surface of the Earth.


Nuclear winter


  In the 1980s, using simple climate models, we discovered that global
  nuclear arsenals, if used on cities and industrial areas, could
  produce a nuclear winter and lead to global famine.
  
  Smoke from the fires would last for years in the upper atmosphere,
  blocking sunlight, and making it cold, dark and dry at the Earth’s
  surface.


Did bombing during second world war cool global temperature

But when we are taking about global warming, oil burning (which releases $\small\mathsf{CO_2}$) contributes towards global warming. 

Why is smoke considered a factor in global cooling when analyzing nuclear winter scenarios, but one of warming when analyzing global warming scenarios?
The question contains a false assumption that climate science fails to consider the cooling effects of aerosol particles, including from smoke, that are the principle forcing expected for nuclear winter scenarios. Climate science does attempt to quantify every significant effect, both warming and cooling - not only the warming effect from increased greenhouse gases - $\small\mathsf{CO_2}$.



Whilst not as recent as I would like, the graphic shows the principal climate forcings that climate science has identified and includes the cooling affects of aerosols.

Aerosols from burning forests are short-lived, and the $\small\mathsf{CO_2}$ from burning vegetation should be drawn back down by regrowth, whether forest regrowth or grassland. The most significant, enduring climate consequence of Amazon forest being cleared and burned is not the aerosols or the $\small\mathsf{CO_2}$ from the fires, it is from land clearing turning a large existing Carbon Sink into a carbon source. 

Turning the Amazon to savannah would release 200 billion metric tons of $\small\mathsf{CO_2}$. The cooling effect of the aerosols from burning will not persist long, but the raised $\small\mathsf{CO_2}$ levels from the loss of a large Carbon Sink will.