Question: why do ssj3 have no eyebrows?
Answer: Him not having eyebrows simply shows how close he is to being as strong as the gorilla state. ... So simply put, SSJ3 is close to the strengh of the gorilla state, which has no eyebrows, so ssj3 doesnt have eyebrows, almost like he would transform into the gorilla, but he can't. (since there is no full moon and tail etc..)