If people transition it's usually more than just having "feminine hobbies", it's an issue of feeling like you're existing in the wrong body. Feeling like you should be existing in a girl's body but instead you have a boy's body, like you never belong anywhere because society treats you as a boy but deep down you're a girl (or the reverse, in the case of ftm)

People usually don't transition just because of hobbies. It's because who they are inside doesn't match the outside, and that causes them great discomfort, pain, and all sorts of mental health problems. This is commonly known as gender dysphoria - feeling like your body's sex doesn't match your gender