Google drive has a grid view option with which the files are listed as tiles/cards and the folders are represented in a small rectangular box at the top. Why is that approach and is there any other variant for it?
Mobile first http://www.themobileplaybook.com/en-us/
Google have been instructed to think first about mobile and fit everything else (e.g desktop) in afterwards.
Folders don't need to be big tiles and on a mobile, if they were, they would take up valuable space. So, for consistency, and with a mobile-first view-point, they should be smaller than the files. Seeing an image of a file will help you quickly determine which one it is (and makes the app feel nicer) so preferable over just text.