Suntour is (ahem,
was) great, and you'll find many fans around here. I'm partial to Cyclone myself.
Short version of their demise, as I understand it, is Shimano beat them to the indexed shifting punch and that was pretty much that. There are others around here that could write a book on the subject, and if you search past threads you'll probably find that book already written one post at a time.
But yeah, that derailleur will likely outlive you and me both. And then the next generation will post another question much like yours. In the meantime, enjoy!