The filepicker takes up alot of vertical space. When it is used in a form in pushed elements below it off the bottom of the page. Because it is large, it also implies (visually) that it is important which may not be the case (e.g. coursefiles).
Maybe it should have a smaller view by default and have a expand/collapse toggle (and get bigger when a drag/drop is in progress).
This issue was raised because of a request to add a filepicker to the assignment settings page - but I am reluctant to do that because it will push important settings off the page.