It's not about karma, really. There are other reasons to upvote things. Over on Mastodon/the twitterlike side of fedi, stars/"likes" don't do /anything/ but tell the OP you liked their post, and are used widely as a social thing. (There is a total star count on posts, but stars don't get federated to other servers besides the poster's, so it's only accurate if you actually go to the poster's instance and look there.)

-- Frost