Why do they keep casting Megan Fox

In movies where her character is naked if the actress herself is obviously uncomfortable getting naked and thus has to "skinny-dip" with tape on her nipples (in "Jennifer's Body") or cover her arm with her breasts in a long scene where she plays a topless angel (this movie).

Megan Fox is just not THAT beautiful. I could make a long list of American, British, or European actresses who are just as pretty, significantly more talented, and have no problem doing nudity. If she just wants to tease "Transformers" fan-boys, then she should stick to PG-13 "Transformers" sequels. I'm not saying this movie or "Jennifer's Body" are great movies, but they both would have been a lot better WITHOUT Megan Fox.