Keep in mind instructors don't really ever get paid 97% of their list price.
Let's say I give you a coupon to buy my course for $19. Technically I would receive 97% of that, but that never happens because Udemy constantly puts it up for $10 and as soon as you reach the course's description page you will see Udemy's "better" deal, and naturally you'll click that.
So instead of receiving 97% of $19 as an instructor, you'll end up with $5 (50% of $10 because you normally only get 50% revenue).
Also Udemy tries to push instructors to make 7-8+ hour video courses which could easily take 3 to 4 full time months to create.
Then of course they play favorites with certain instructors. For example it's not uncommon for Udemy to reach out to certain instructors and then go into a bounded contract with them which basically says "look, if you make a top quality course, we'll promote the shit out it for you. We'll even give you a direct internal contact and resources to help you make the best course possible for this niche." which essentially means if you're NOT part of this, it will be impossible to compete with someone who is because the biggest factor in ranking well is number of sales + number of positive reviews.
Long story short, I've spent a few years teaching on Udemy (and even made decent $ on it without any special treatment on Udemy) but I'm slowly trying to remove myself from them because of how poorly they treat instructors.