Adjuncts are necessary to the university, but their pay is dismal at best. Benefits are not enough to make up the difference. The attitude is that "if you won't do it, someone else will." For a position that requires a degree, the pay is not only insulting but not a living wage. Combine that with the fact that you must disclose any other work you do outside the university, and your file is flagged if you do! It is a trap.
On the other side of the coin, if you love teaching, the work is amazing and fun!