This is something of a catch 22. You normally won't get hired for a job that's completely out of your expertise, unless, by a stroke of luck, you know a lot about the field, worked in it before, or have personal connections to someone in it.
Thus, if you got the "wrong" degree you have to dump more money and time into going back to school for a new degree with no guarantee of a job when you graduate and twice the student debt.
As PredatorX mentioned, many employers only hire people with prior work experience at that job, so even if you got a second degree in the field, you aren't qualified to work in it.
I agree it is somewhat of a catch 22. Just because you have the education doesn't mean you get the job. Still work history can get you a foot in the door.
Another problem I noticed with my generation, is that they don't want to start at the bottom. They have the education and the want to get the high paying job, they want to be the boss and they won't take anything less. A part of my program is management.. I have had interviews with many employers and often the first things they tell me is, I am not going to be running things, that I will have to do my time at the bottom.
Did a co-op with other college and university students going to school of much the samething as I am. I was a couple years older then them, and they would not shut the hell up about how low they are being paid. "I am going to school for this?!" I would turn to them and say "you have zero experience, did you honestly think you would be running the place?" It was good they complained alot, made me look good because I did what I was told and didn't complain. I was given more trust then they were.
So the point is todays generation often doesn't want to start out on the bottom. They often go to school for useless things, that have no real world application. Or if they do have useful education, they don't want to work their way up the ladder.
Young people noadays feel entitled to everything, that they should just get the high paying job.