Student-loan interest is resuming. Here’s why the government charges it.

For more than a decade, Robert Layton has been making payments on the roughly $128,000 he borrowed to pay for college and graduate school. In that time, he estimates, he’s paid about $63,000 — $45,000 of that in interest. 

But the current balance on his government-owned loans stands at $219,000.

Layton, who works in IT, graduated in 2009….