1. The development team really didn't consider it an exploit. Yoshi actually stated that it wasn't easy to do the BLM burn and not just anyone could do it. Also it was Golden Week and taking down the fight would not have been fair to those who were capable of beating it without BLM burn
2. They get rid of people who bot that directly alters game mechanics. Also their budget is running dry since they are making an entirely new game from scratch while working on this one so they cannot afford an anti-botting task force like in FFXI.