One thing to keep in mind before going in to the rest... Most student loans are backed by the federal government and are not dischargable in bankruptsy proceedings etc.

In terms of corinthian and most of the forprofit colleges.. Basically they were given the green light to operate as they were for years by the federal government which backed the Student loans.

The colleges themselves for sake of their margins of profit misrepresented themselves their student career success figures, were generally predatory in their recruiting practices(got caught trying to signup mentally disabled people at an army hospital head trauma ward), lied to their students about a lot of things and utilized the federal student loan system for sake of profiteering. This was done with little to no oversight or accountability from the end of the federal government.(for decades technically)

Once attention was called to the low graduation rates, poor post graduation career prospects, predatory practices(they got caught trying to recruit out of a military hospital head trauma ward) alongside excessively high student loan balances... nothing was done for years.(cheers for corporate lobbying) Basically it is in the interest of the forproffit college to provide you the cheapest product they can, at the highest price while keeping you a captive student for as long as possible with 0 regard to what hapens to you as a student post graduation or wether or not you graduate at all.

So, as to

Why should they get loan forgiveness?

Because the students not only got fucked by a scammy forproffit institutions they got done so with the governments approval. Now, since the scammers have been called in to account and with them going out of business the students wont be able to complete those degrees corinthian as an example has been forced to give their students full refunds for current coursework and to also refund student loans.. the government agencies that approved for their actions in the firstplace have also started to stepup. So, as to why.. well because not only is it the morally right thing to do it is also legally the right thing to do aswell.

Though from the governments perspective if someone graduated from one of those shamschools that still counts as a degree earned even if it is a worthless one. So former graduates are still kind of fucked.