I think @mrs.steemit is right that video length matters, as a lot of people either don't have the time to sit down and watch a long video or just don't have the attention span, that's the world we live in..
On the other hand this post clearly shows that vote count quickly becomes decoupled from actual views even for short videos. Part of the reason for that is people who have a lot of accounts and automatically vote with all of them, I tend to do that for example. So say I watch the video and vote with my main account, that triggers voting from 2 of my other accounts.
Another reason is what @craig-grant said in a comment here that a lot of people, especially some of the whales, have this miner mentality where it's all about maximising profits. So they vote automatically for certain authors and setup bots to maximise their curation earnings and basically milk Steem for as much profit as they can. Unfortunately there's not much we can do about this at the moment, although the vote recharge changes that were postponed/cancelled might've helped with this. Making voting power more of a scarce resource would make "spam voting" harder which is a good thing in my opinion.
The reason videos don't autoplay is to optimise the performance of opening a post, as loading lots of videos will slow down the rendering a lot. What Steemit does now is simply render a static preview image that you have to click on to actually load the video, it lets the page load a lot faster.
I know Facebook autoplays videos in your feed when you scroll over them and that might be an option in the future here too, but I'm not sure it would really help with people actually watching the videos to the end. I rarely watch the videos on Facebook to the end even though they start automatically. There's a bandwidth concern there as well of course.