Adjunct faculty are the serfs of the higher ed industry. Generally speaking, and excluding the "studies" hires, these are very bright people who have either lacked the genius, or the political savvy, to achieve the cushy life of academic tenure. They also tend to be people for whom, ironically, life outside the non-profit bubble seems frighteningly competitive with frighteningly-measurable results.
I once imagined the idea of an academic life, but quickly learned that I was not a genius even though I have some flair for teaching and perhaps a bit of a calling for it. I might have been a beloved and valued private secondary school teacher, but that turned out not to be my fated path. It could be a good retirement path for me, however. I could teach Civics, history, Art History, Law, Latin, and Government, and I can coach Baseball and Soccer. That won't happen, though, because life is too short for everything and retirement from my post is not on my agenda. I like being the boss of me and I do not like answering to anybody.
A Harvard writing instructor discusses 'The Great Shame of Our Profession'