You should reread what you wrote.
That’s your answer right there.
You know what your passion is, but you seem to feel that it is not something that is worthy of your time and energy. If you are passionate about writing, why do you think that the only thing that is worth doing with that passion is writing about business?
It seems to me that somebody (or somebodies) has (have) been filling your head with nonsense about having to engage in ECs that will help you get into a “prestigious” major, and that your real interests and passions are only important so far as they help you do that.
In all honesty, the way you express your “interest” in business, you seem to have no real interest in business at all. You seem to want to get a degree in business, while actually engaging in writing. Both your mention of marketing, and your idea of a “Business EC” being a blog, are strongly indicative of this.
You love to write. Do that. Attend creative writing workshops, be part of a short-story/poetry/novel writing/reading club or clubs, submit your writings for competitions, etc. Limiting your writing to a blog about business is such a meager way to engage in such a passion.
If you want, check out some business related ECs as well. However, do not engage in ones that are actually all about writing. If you want to explore this interest, do so, but actually explore that interest. Don’t pretend to be engaged in business while you are actually just engaging in another writing EC, because that won’t tell you whether business interests you.
Good luck!