We had a race in Louisiana in which one candidate touted they were more qualified because they had graduated with 4.0s from college and law school. Sounded good, but the candidate had taken 10 years to get through college taking 1 course a semester and 6 years to get through law school taking 1 course a semester. Only seniority in Judicial experience is truly an objective criteria. That means that people take little interest in them and in who is running. Name recognition becomes everything.
TV means money.
Bar none, TV is the least costly method of reaching the most voters. It is cheaper than mail. The corruption arises not because elected judges are necessarily dishonest. Corruption does not arise because elected judges pay back political support. The result is not a court, but a legislature.