> Im guessing the answer is probably Java is why eclipse is out of favor.

Some people just want a text editor, whereas eclipse is “an IDE and Platform”.

I don't think that's really why VSCode succeeded or Eclipse failed.

Eclipse failed because it was slow and janky and had abysmal UX and it only supported Java well.

VSCode succeeded because it has a much more sane UX, it's way less janky, it's highly extensible and language neutral.