Until you are found guilty in a court of law, or admit to your guilt by paying the fine, an outstanding traffic fine is nothing more than an allegation of wrongdoing. As pointed out, you cannot be arrested for an outstanding traffic fine because you have not (yet) been convicted of the offence of which you are being accused in the fine.
What you probably find is that the people who are being arrested for "not paying their fines" are more likely being arrested because a warrant of arrest is out for them for contempt of court because they never pitched up to their court appearance for the fine.
What you probably find is that the people who are being arrested for "not paying their fines" are more likely being arrested because a warrant of arrest is out for them for contempt of court because they never pitched up to their court appearance for the fine.