When navigating, I of course pay close attention to where my cursor is. When I scroll to read through lots of text, I'm not moving the mouse cursor randomly around the screen, but I'm also not paying attention to where it is because scrolling up/down behaves the same regardless of where the cursor happens to be. On a site like Wikipedia, this means that my cursor can happen to trigger a preview hover that covers the very text I'm trying to read. Even if it's in a different spot, the movement is enough to be annoyingly distracting and often means I lose my place.