What do you think happens when people refuse to pay fines, jail fees, and court costs? Or child support, wage garnishments, or back taxes? They certainly don't just send you on your merry way. In some jurisdictions they have to have a court or judge look at someones ability to pay instead of automatically jailing them for failure to pay fines, but whether they are arrested or not as a result of that is completely at the judge's personal discretion, and many judges are selected specifically because they are hardasses that earns the local court system/county money.