Merchants Guild misunderstood the sealing of dungeons. They think that if the dungeon is sealed, it will disappear completely, but it doesn't. Dungeons that have been sealed do not mean it disappeared and cannot be entered, but the number of strong monsters will not increase significantly. So, weak monsters still exist, and some of them can be used as a business, such use their fur for clothing materials. Areas that are "clean" can be used for plantations or livestock. Business from adventuring will decrease (not disappear), but the business as a whole will not destroyed.