Sometimes they are great sites, but the owners want too much money for them and will probably get their price someday. Most often, however, the site hasn't been built on because of difficult topography or some other natural barrier to construction. In other words, it would cost too much to develop. With unique development comes some unique problems. Trees are removed.
Drainage becomes an issue.
And worst of all, folks become enemies before they become neighbors. Of course, the City is usually in the midst of the controversy because we are the regulatory agency. What typically happens is that we do all we can to make certain that codes and construction requirements are followed. Sometimes that isn't enough and neighbors want more. Then it becomes a civil matter and attorneys need to enter the fray.