Most of the time it’s the echo chamber needs that we all have, we want to see opinions that match our own at the top, and opinions that don’t match, at the bottom.
The issue is that social media is very aggressive on the trends. It’s easier for people to formulate a judgement (when the opinion is somewhat ambiguous, or not very strong) when someone else has done the actual judgement for you and upvoted/downvoted.
If votes where not shown at all, the comments would have wildly distinct amounts of support. It’s a pretty fun subject to study to be fair since it affects all of us very strongly so they are not just fake internet points in that sense. People’s days are sometimes dictated by the amount of validation or hate they get from strangers, we’ve been seeing this since Facebook and it will continue getting more relevant as we move more of our daily lives and activities to the digital world.