For me its whats look cool that matters, I see Cobra as a millitant political movement and as such they dress in a way they (and or Cobra Comander) think is cool not necessary what is the best. Also I suspect Cobra does it to save cost, no need for diffrent camos for desert, winter etc when everybody wears blue all the time.
That said in my Joverse i have cobra divided by cells and the reason they have so many diffrent troop types and uniforms (even overlapping eachother in some cases) is because they are getting their equipment from diffrent places.