That answer is still begging the question of why it matters that bankruptcy rates stay low.

It's obvious that bankruptcy costs the lender, but how that cost gets absorbed is very important here. A mortgage or a car loan are secured debts, where the lender can repossess and sell the collateral, to pay off most or all of the losses if the borrow defaults on the loan. A student loan is an unsecured debt, so any defaults have to come out of the interest of the rest of the borrowers serviced by that loan program.

The more borrowers default on their payments, the higher the interest rate is needed to cover the write-downs. Without any protections against defaulting, interest rates would have to be near those of credit cards, while limiting when student loans can be discharged limits how much needs to be written down, which keeps interest rates lower.

Higher interest rates would not only make student loans cost more, it would also reduce their availability and increase the default rate, which could create positive feedback, causing the rates to increase significantly faster than inflation. Combine that with incentivization for college attendance already causing tuition itself to increase significantly faster than inflation, which itself makes student loans increasingly necessary, allowing student loans to be discharged during bankruptcy could have compounding effects on the fragile system that currently props up college attendance rates.

That still leaves the question of why the government should incentivize a significant portion of their constituency to be in college, (more than 1 out of every 13 US adults are currently enrolled) but I'll have have leave that question for politicians or maybe even voters.