Nietzsche continues to stick around
It's the moustache.
I think a lot of the commercial appeal is 1 "Thus Spake Zarathustra" is a cool name, and (2) there's a market who want to say that they have read the philosopher who said "God is dead."
There's a coolness factor to things like "what doesn't kill us makes us stronger" that's about as far as most people get.
Agreed on those, too.
You can buy Nietzsche and have him on your bookshelf and make people think you're countercultural.