I think it takes more thought to decide whether to upvote or downvote a post than it does for a comment. A comment can be bandlimited, focused and directly or tangentially related to a post, upvoting it doesn’t necessarily imply endorsement/validity of anything other than the specific content of the comment. Upvoting a post/link on the other hand takes a deeper consideration over the full set of things you are endorsing/validating as true by upvoting since what is under consideration isn’t a contained specific statement set in the specific context of a conversation. Consider a link to an actually halfway decent article on a very problematic website, upvoting the link becomes a quagmire of thinking through ok well maybe this article is accidentally saying something useful but what is the context here? In contrast upvoting a comment about the article that says “I agree with this article for the most part, but fox news isn’t a trustable source!” by comparison takes much less mental friction to calculate out for yourself.

Also I think the comments just tend to be very informative here, they are why I am here in the first place after all and not just going directly to where the links are posted to. Naturally this will lead me into following a conversation and upvoting/downvoting based on how I react to the conversation in a way that feels more important than the overall link because it is. The link is the starting point to a broader potential conversation and I think it is natural to be more focused on that when after all that is the entire point of this structure of social media. We would all be reading RSS feeds alone if we didn’t care about the comments.