Using the allegory of Ashton Kutcher and Demi Moore:
It sounds cool at first. She's still hot and has got it going on to attract a young man. A few years pass and then she starts having concerns that he cannot relate to just yet such as menopause, gray hairs, and routine examinations like mammograms and colonoscopies. If this woman was able to freeze who she was at age 40, then things would be going swimmingly, but she cannot.
Taking this same example, imagine if someone that is in their early 20s takes out tens of thousands in student loan debt and they pay as they should. They may well be paying it into their 40s or 50s depending upon how much they took out and all of the other factors that one considers such as not being able to find a job that pays enough to pay it off quickly. Around this age, health concerns start creeping in, but the chances that this person is going to be struck down by something catastrophic are present but not as great, and they have to contend with the possibility that they might be laid off and have problems finding a new job because of ageism. Still, there is a better possibility than not that the majority of whatever amount on the loans they have left are not going to balloon into the tens of thousands from a default. By that point, they will (more than likely) be relatively paid off even though they have been haunting that person's dreams for a couple of decades. Your children will also start going to college around that time, and you are in a better position to help them since your loans are either paid off or nearly paid off.
Imagine now what happens if that same person takes out that amount of debt at age 35, 40, 45, etc. It sounds cool at the moment because they are young and can keep up with the 24 year olds when they go out and drink after class. However, that person will more than likely encounter ageism, so their job opportunities won't be as great. Even if you land a job and stay in it for a few years, there is an increased risk of being laid off and having an unusually hard time finding a new job. This new job would likely pay a lot less than the old job.
Even if you manage to overcome that and do reasonably well, your chances of developing a chronic medical condition that requires expensive management may occur. Now, instead of funneling the money to student loan debts, you're having to split it with your diabetes and high blood pressure medications as well as the doctor's visits that come with that.
Furthermore, if you had children, this also means that you are still paying on your loans while trying to pay your children's loans if they go to college.
Unlike Demi and Ashton, you can't run off to the court house and have the arrangement voided. These are yours forever...and ever...and ever...and ever.