I don't think there's any valid inference from "thinks the poll worth voting on" to "thinks the comment with a poll in worth upvoting".

Suppose I see a poll, think it's a reasonable question to ask but no more, and am feeling helpful. Then I'll likely fill it in. But why does that mean I should be upvoting it? I mean, if I see a comment, think it's a reasonable thing to say but no more, should I be upvoting that? That would seem to lead to the conclusion that most people should be upvoting most comments, which seems waaaay off to me.

I upvote things that seem to me especially interesting or insightful or useful or witty or whatever. A poll can easily be worth filling in (if only because whoever posted it presumably is interested in the answers) without meeting that condition.