It's not that they don't do it because it takes effort, it's just a long process for them to get there. I have personally known someone whose paychecks were being garnished because they defaulted on 5-figure student loan debt, but he said that he ignored calls and letters for years and then ignored months (maybe even a year plus?) of court summonses to get to that point.

I was helping his wife fill out IBR paperwork and offered to help him with his and found out he had to be in this forced repayment for some period - couple years? idk this was ~10 years ago - before he could even apply for anything like that.

It's an evil trap, and they really will come destroy your financial life.