IBM is often known for having an NIH (Not Invented Here) mentality, so they invented their own GUI classes. But in fairness, SWT is widely percieved as being saner and faster than AWT or Swing anyway.
Eclipse is written using SWT, but a number of people also have built apps of their own using the SWT UI. There are even some Eclipse plugins that can help you, some of which generate to AWT, SWT, and even things like HTML.
An IDE is no substitute for an Intelligent Developer.