I took a quick look at my news feed, and found that non-sponsored "full screen" posts are very common. A few recent examples:

http://i.imgur.com/zcHoH.png

http://i.imgur.com/khR3W.png

http://i.imgur.com/zFdyv.png

http://i.imgur.com/fF8EM.png

Obviously, it's very popular to share photos and videos on Facebook, and it's understandable that those forms of media will take up a large percentage of small mobile screens. Not really an issue specific to advertisements.