For treatment of burns, why might bacitracin be favored relative to silver sulfadiazine even though its antimicrobial coverage is less broad?

because silver sulfadiazine causes:

• allergy in patients with sulfa sensitivity
• permanent silver staining of the skin and therefore should not be used on the face or other cosmetically sensitive areas
• severe hemolysis in patients with G6PD
• sulfonamide kernicterus in children less than 2 months and therefore should be avoided in pregnant women, newborns and nursing mothers

Source

Hall, R., Watts, L., and Bashiti, S.  "Thermal Burns"   Critical Decisions in Emergency Medicine.  March 2012.