Here's why:

1. it's just not allowed. See our Terms & Conditions.
2. the acquired Student can report you for this at any time. And if they do, you are liable to prosecution. Is that really worth it?
3. it may be convenient for you as a Teacher but may be less convenient for the Student i.e. on our platform they have a guarantee,
4. you would have to create, market and sell your Courses on your own,
5. you would have to spend 'unpaid' time selling and pitching your Courses to potential customers,
6. you may not have the exposure to lots of potential customers who come here to find the right teacher, coach, consultant or expert in the field,
7. we'll make sure you'll miss the convenience of using our platform by continuously improving the user experience on our platform. That's a guarantee.