Mr. Pahs: "People" aren't choosing which laws to follow, the local authorities are choosing which enforcement actions to prioritize. 

The police cannot enforce all the laws. They don't have the resources, so they must decide which ones are the most important to enforce and which ones are less so. If a police officer is trying to stop someone who just sped through a school zone, they aren't going to stop mid-chase and ticket someone for littering. Given that immigrants, whether documented or not, have much lower crime rates than US citizens it makes sense to not focus on them.