uberninjaa is right, most of it is lack of forethought. The joke is associative and unsurprising, leaving the viewer to make the leap of faith that it's funny. Applying reason can reveal it's not at all funny, but that's not the point.

The point is the voting system here, which is abysmal at best: reminiscent of a classroom voting for class leader: it becomes a mindless popularity contest where whoever seems like they are getting the most votes gets disproportionately more votes because voters want to be on "the winning side". People don't vote with their principles, which in governance is often the case.

In the US, we elect representatives which (historically) have promised to vote with their principals over popularity. This gives our democracy value: whereas the class leader example is just tyranny of the majority. People end up bullied into voting for the "right guy" because they see everybody else vote for them. This is also due to single vote system instead of voting for the person you want the most and the second choice (which is a better system). People overvalue their vote and thus waste it.

As for reddit, there are people voting for this and people voting against it, people who like it but won't vote, people who hate it but won't vote, and people who never see it in time until it reaches the front page. Even then unsubscribing makes it invisible. (I bet a ton of redditors register simply to unsusbscribe from /funny--it takes up the majority of the front page and a lot of those front page posts violate the so-called rules of the subreddit).

That said, if you have something to say on the topic, you probably thought about it at least minimally, so chances are you either didn't vote (like me) or hated it and downvoted. Although right now it seems like it's only up by a thousand, with 5,000 against and 6,000 for. That doesn't seem too unexpected. Even though more people like it, a huge hunk of people hate it.