User blog comment:DarkStar Knight/Things About Monster Hunter I Would Change/@comment-3111150-20101107065426/@comment-1203191-20101109125659

Well I guess because sheaths for fire weapons would most likely be made of an insulating material to contain/absorb the heat. It can't be on fire if its in the sheath, because fires need oxygen to exist. And its not a continuous fire, it only ignites with each strike, so that would also help prevent fire weapons from overheating.