Sometimes, schools will ask you to explain how your personal and professional experiences lead you to these specific goals, and in this case, you should explain them. Otherwise, there is no obligation to explain them.
i don't think you can completely avoid talking about why you want to pursue this particular career goal in your essay. always be prepared to answer this during the interview.
我也是转行的,所以我觉得我的职业目标的essay主要就是要说为什么要转到这个行业中,联系自己的背景和经历给一个合理的解释,并且能够说明为什么我是独特的,为什么我的目标是具备可操作性的,我有什么潜力实现这个目标,MBA能为我实现目标带来什么。就是说,why the career goal 是和Why MBA,Why now,Why this school联系在一些的。
The "why" and the "how" is infinitely more important than the "what". "Why this goal" is, as you say, difficult to write about directly, but reading your entire application it should be clear what defines you as a person, and why you chose something.