Most folks are "proper" members of society. They have jobs or at least something they do regularly like begging on the street corner, families or loved ones or a groups they are somehow responsible for, and make their way in the world pretty much where they are. Heck - even brigands and bandits fall into this undesirable but "functional" category. Then there are those who don't fit in with the rest of the folks.
Of the misfit group those that have the ability to gain levels and be adventurers almost all of them do so. The utterly wretched remains are those desperate and foolish enough to allow themselves to be hired out as henchmen for adventurers.
Henchmen are dregs and they know it.
All of this information has been updated and replaced in this post. Here is what you need to know - the tables were nasty and all the henchmen were probably too terrible to bring along on an adventure.