I got linked to an interesting infographic about adjuncts teaching university courses in the US. There is plenty of data there but the summary is that people graduate with PhDs in great numbers and the vast majority of them cannot get a highly paid position as a tenure track professor at a university. They usually end up teaching as an adjunct which in many cases pays less than a living wage and is a miserable job experience, particularly for someone who is loaded down with student debt from earning their PhD.
There are plenty of things going on here but I think the biggest one is simply that there are too damn many PhDs graduating compared to the demand for them. You could blame the institutions for graduating far more people that could ever be hired for tenure I suppose, and that has some merit because it isn't like people getting a PhD in English Literature are all expecting to work in industry. On the other hand I think a lot of people getting PhDs are doing so because they haven't done any work to find out how dismal their job prospects are so blaming them also has merit. If you are going to spend a fortune and eight years training for a job you had best spend a few days working the internet and your contacts to figure out what you can realistically expect when you get out the other end.
In any case the result is huge numbers of people begging for teaching positions of any sort and that leads to abuse by the institutions hiring them. If you want to see this situation remedied very quickly just stop anyone entering a PhD program for a decade. When the young and desperate folks suddenly dry up institutions will discover themselves having to offer a decent compensation package and security to those they wish to hire. Clearly that isn't going to happen though as there is a neverending supply of people convinced that they are special and that they will beat the odds.
The mindset of "Well, *I* am special, so obviously I will beat the odds and succeed in a field of brutal competition." is endemic in a variety of fields. Music, professional sports, acting, and of course post secondary teaching are examples. This is why you see all kinds of aspiring actors waiting tables and why you see aspiring tenured professors taking a position as an adjunct for pathetic pay. That extreme risk of failure is a price you pay for being involved in a desirable field. You want to work desperately hard to someday become an accountant? It is a good bet that someday soon you will be working as an accountant because that field isn't glamorous.
It would be great if institutions would simply pay and treat their adjuncts well. Unfortunately that is a tricky thing to arrange when there are hordes of people willing to work even when they aren't paid or treated well. What we really need is the general perception that a PhD isn't a ticket to a great job but rather just an opportunity to spend years doing research for no pay. That would cut enrollment enough that the system might just right itself - good luck getting there though.