Why are ninjas smelling bad?

Answer 1

Ninjas dont smell, it would impair there ability to be invisible at all times

Answer 2

Ninjas are often depicted in pop culture as being stealthy and elusive, so the idea of them smelling bad is likely exaggerated for comedic effect. In reality, ninjas would have been trained to be clean and to avoid being detected by enemies through any means necessary, including maintaining good hygiene.