I'm faculty at a regional university in the U.S. Our enrollment is dropping by 5% a year, and short term positions are becoming the norm. Tenure track positions are risky in that once you've got somebody with tenure, it's difficult to get rid of them (intentionally). Short term positions give universities flexibility. We are not a Harvard or Yale with billions of dollars in endowments. Tuition is 80% of revenue, and our existence in 20 years is in no way guaranteed.

I don't know how many universities are flush with cash and are just being stingy by using adjuncts, but where I work (small regional university), we have intense budget pressure. We'd have to raise tuition a lot to cover the cost of converting adjust to tenure-track positions.

I don't like how adjuncts are treated, but seeing the problem from our administration's point of view, I know why we have so many adjuncts.