What you believe isn't really compelling, but public ignorance is true force of nature.

> I think I'm relying on the fact that a lot of people feel a video-based lecture works better for them, than static documentation.

People who sign up for a video course about computer programming very clearly do not understand computer programming. Imagine one of the students applying for a job as an IPython expert and saying, "I took a video course!"

This is not how people learn these kinds of things, in more than a superficial way. But it is a way for businesses to make a lot of money from ignorant people.

> It's not $10 per video. You pay once, and you get the whole course.

False. Each section is $10. Each course heading has a title, a duration, and a requirement for $10. Did you bother to look at the graphic I posted?

> That's a UX problem with Udemy.

I'm sure that a dissatisfied customer will prevail in court, saying, "even though each section was priced separately, I was given to understand that $10 covered everything."