Along with the rich enterprise libraries that come as part of the language, one of the biggest advantages of Java is the vast number of third party libraries available. For example if you are writing an enterprise web application, GWT, Spring and Hibernate provide a framework with a huge amount of pre-existing functionality.
The size and number of dependencies grows as your application grows. GWT and Spring alone, without their dependencies, are more than 7MB. The ideal place to put dependencies is in a source control repository as part of your project so that when you or your continuous integration server check out the project for the first time all the dependencies are there. Then you don't have to go and get them and store them locally in a location that is agreed by the entire development team.
Storing the dependencies for a single project in a source control repository isn't too bad, provided there is plenty of room on the source control server.. However, if you have more than one project using the same or similar sets of dependencies the amount of space taken up in the source control repository starts to get a bit ridiculous. And then when a new version of a library comes out and you upgrade, even more space is wasted as the differences between binary jars cannot be detected, so the entire jar must be replaced.