These actors (Gosling and Cruise) just don't have the right frame or bone structure to carry much muscle. They're meant to be slim and keep low body fat levels. It's just the way they are genetically built.
Luckily, they were genetically gifted with the right look (face) that lends itself to what Hollywood wants/wanted.
Also, women don't care about muscles on a man as much as men care about muscles on other men. Although illogical, it is most often true. Doesn't mean that the men are gay for being fixated on the build other men have, but instead could possibly be the way we are hard wired. I have no evidence to back this, but sometimes I think that at a carnal level, men look at other men with muscles symbols of strength, leadership, manlihood and fertility. I can even see where subconsciously men with less muscles could look to other men with the right facial features, frame and muscles as a guide to more manliness. I think this much is true with children and youth (teenagers and even young adults in college).
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