It used to be that Swing/AWT really sucked. The default theme on every platform (Metal) was really ugly. Everything was purple. The "native" look and feel was emulated (poorly). It was also very slow. That's the reasons why SWT was started in the first place. Swing would just not cut it for any app that wanted a nice UI.
Nowadays the situation is completely different. Swing looks and performs great compared to SWT. IMO it would make much more sense to just use Swing.
JavaFX never happened. People just went web instead. No one uses it and it's officially deprecated.