I can't imagine a world where anyone would care about their Reddit account karma. I periodically destroy any Reddit account I have to use as a matter of online hygiene.
(and yes, I destroyed the account I did an AMA on a while back as well.)
Come on. You have to know some people care about their karma. Reddit being one of the biggest sites in the world makes that fraction of people quite a large number.
I wouldn't say I care about it on HN but it is a site topic (programming) that is relevant to my career, so it aligns with my interests. Reddit is just.. irrelevant.. to basically everything. It's fine for entertainment at best.
(and yes, I destroyed the account I did an AMA on a while back as well.)