Because the Garmin GPS system …

… is leading some drivers … straight into a dead end. …The electronic maps don’t show a gate that separates residential and industrial areas. It’s only opened for a couple hours on weekdays in the northern New Jersey city.Mayor Dennis Elwell says residents on Fifth Street started complaining about trucks clogging their street about a year ago … Some drivers have to call police to open the gate because their trucks are too big to turn around.[source]

This has led to a call for Open Source GPS databases.