That history is why they're bothering with a prosecution at all. Otherwise there'd just be a case file to establish a pattern of behavior for the next time he screwed up. They may "know" that he was driving under the influence, but they have no way to prove it to a jury (a useless witness and probable drunkenness--with no breath or blood test--on a phone call long enough after the fact for him to have gotten drunk after getting home even if you can prove he was driving wouldn't cut it even if Jon were some no name with a public defender) and the actual charges are the kind of charges that are never prosecuted for their own sake even with solid evidence because it would be a complete waste of time and resources better spent elsewhere. In isolation, this case is a complete loser that isn't worth the prosecutor's time.