If its broke don't fix it is an apt description of problem with the student loan system. While it's not perfect it does function as it's supposed to.
It's a pattern in every day life. A door squeaks on its hinges but still swings open, a shirt full of holes that's perfectly fine to sleep in. Whether from laziness or a lack of knowledge, if things are at least functioning rarely do they go out of the way to fix a minor inconvenience. It's bearable to live with. The same can be said for global workings.
While some global problems definitely need immediate attention and fixing like oil spills in the sea and disaster relief, other things people can wait on. It's the same idea that goes into tarring holes in the road instead of ripping up the road and replacing it. It's a time consuming process and over time, even if there's something new, it'll be worn down, show problems, and have to be revised and fixed, sometimes being better or worse.
The main problem is that people don't want to wait that long. When a 4 lane road goes down to a two lane a persons time is wasted, there's a back up of traffic and people get mad, usually at the wrong people. It's chaotic, troublesome, and leads to expensive problems no one wants to deal with.
Replacing the student loan debt system is a major uptake that is costly, takes time, and would have people getting angry despite how the revisions are for their benefit. Unless a concrete system that's proven to work and can seamlessly replace the original system is devised then it'll be very hard to get people to agree to wait patiently as changes are made.