User blog comment:A2707/Fletch the Flaming Bowmaster/@comment-188.178.209.202-20121127221413/@comment-2223363-20121127224634

Because... well, it messes up with last hitting, no? Due to it's DoT nature, you have to calculate better your last hits. Also as Burn cannot stack, when using his ult it might be better to apply a stack, toggle off then after 3 seconds toggle again. The toogle cooldown easily allows it, since its only 2 seconds when you toggle on (thus toggling off has no cooldown).