Why Elect judges?

One thing I never really understood about the USA is this need to elect judges. In Europe, where I come from, judges are by and large appointed according to how good they are for the job, rather than for political reasons. In other words, what counts is how well any prospective judge knows the law.  The politicians make the laws, and the judges simply decide whether these laws are being followed, don't they? Having elected judges certainly makes them accountable to the public, but how is there public to know who is a good or bad judge? Moreover,  candidate judges  have to bend to popular undercurrents and special interests.  A weird procedure. Hey, why not elect doctors and professors as well?