In my opinion the upvote system gained popularity not as anything like an effective means of content ordering (
even if that was its original intent) but because it's an effective means of site growth. It turns discussion into a game where you can get, or lose, points and creates an emotional response system not all that dissimilar to the blinking lights of a slot machine.
An interesting thought experiment. Imagine a site like Reddit disabled all external numeric displays of score for a year. You'd only have indirect indicators like order prioritization and apparent visibility based on the number of comments responding to a post. Would usage increase or decrease relative to what it would have otherwise? In my opinion it would not only decrease, but somewhat precipitously. There are a vast number of people that seem to participate almost solely as a means of increasing their score. And even for those not fully addicted to the system, it certainly provides an emotional feedback mechanism. Without this, I do not see these users participating as much - nor do I see a sudden influx of others to replace them. On the other hand, I also imagine this would likely substantially increase overall quality. Like you mention low effort content that incites a reaction is a hallmark of gaming these score systems.
