The sociologist in me suspects that scoring systems are popular because they instrumentalize interaction in a sufficiently ambiguous way to do work for many audiences. It's really useful that comment scores have vague relationships to a lot of socially important qualities (interest / sentiment / etc). I 'use' changes in my HN karma as a cue that someone is interacting with one of my comments. For me the karma system could be totally replaced by reply notifications - but others might use it differently.
Keeping the score system basic leaves each person to have whatever thoughts they want about their karma without the website telling them how to feel. There's a dark pattern aspect to this where web sites can foster unhealthy levels of interaction while saying that's not what they intended. There's also an emergent behavior side where scoring systems are used in ways the makers can't predict.
The cynic in me says it's just gamification to maximize site owner's net worth.
But maybe it's like "teaching to the test", where if you're teaching to a well regarded test, you're actually doing a good class.
Extending the analogy, if the site's value is well aligned with your self-value (quality of the test), then playing the site's score game (teaching to the test) may be beneficial to you?
Here's an example: I invested some time a few years ago to improve the quality of a few Wikipedia articles. I later found very similar reasoning to what I got into these articles in legislative debates. I think I had a hand in influencing something important to me by updating Wikipedia.
I totally agree that many sites put the scores in to maximize revenue. I'm just trying to consider scoring systems in the wider context of user <-> website interaction techniques.
If score systems were just to generate revenue, I'd imagine that users would have a roundly negative view of them like dark patterns that help revenue (spam, tracking, sponcon). I think you're absolutely correct about scoring systems reflecting your position in the ontology of the sites' creator, and so if you want what the site wants you want your score to go up. I suspect that the popularity of scoring systems comes from users understanding they could be bad or good and being drawn in to the enjoyable play of discovering what their score reflects based on their own experience.
I am with you on the karma being about the same as a reply notification for me, but then I don't care how many likes my holiday photos gets on Facebook.
I know people for who these systems has quite the negative impact. Below are two examples from Facebook.
Example 1: Someone gets really depressed if they don't get about 10+ likes on photos on Facebook. Positive comments are ignored in favor of the number of likes.
Example 2: Someone got really upset and depressed that only a few people wished them a happy birthday on their Facebook wall. Everyone else had done it either in person or via private chat, yet they went down the "no one cares about me" rabbit hole.
Keeping the score system basic leaves each person to have whatever thoughts they want about their karma without the website telling them how to feel. There's a dark pattern aspect to this where web sites can foster unhealthy levels of interaction while saying that's not what they intended. There's also an emergent behavior side where scoring systems are used in ways the makers can't predict.