see attached image, but basically having the images on the right side makes it so hard to "read" a post with an image, going back and forth with your eyes to "get" the whole post. So much easier to just put the images between the up-/downvote buttons and the text post.
I don't know if there's a reason for that besides looking different from similar sites. If so, I don't think this is the way, it really puts a strain on your eyes and our brain is not used to absorb information in this way.
Not sure if expanding an image like that would be possible with pure CSS/userStyles, some actual code might be involved there
but you CAN use CSS to scale the image upon hover, which could at least help with desktop usage.
Or you can move the button to expand the image also to the left/right depending on where your thumbnail is.
That's basically what I liked most about the Relay app for Android - easily switch between left and right depending on how I hold my phone.