You're probably right. But I feel like that's learned behavior because over on Reddit and Twitter, likes and upvotes/downvotes held so much sway over the algorithm because that's what advertisers wanted, here there are no advertisers, so why not fix the shitty training they forced on us?
Why is it shitty though? I personally want a site that disencourages people that I don't like (like right wing trolls) from posting. We're all here for our own reasons. We should all collectively be able to decide what it is that this site encourages from it's posters. A really well thought out post from a Nazi is something I don't even want to think about.
It's not training. It's quite intuitive. Voting for/against something is common in many scenarios, not just from Reddit. And most people will associate up with good and down with bad.
If you like something, you want to reward it, and if you dislike something, you want to do the opposite.
With the vote buttons right there, it was inevitable this is how it would end up.
Even more logically, people know that higher-voted items get more visibility and lower-voted items get less, so if you like something you're more likely to want others to see it. Therefore, upvote it to send it higher up the tree. And send it down to hide it.