FYI, the "why not just learn from a Khan Academy / MIT OpenCourseWare / a textbook / etc" question comes up from time to time, so I wrote up a detailed answer here: https://justinmath.com/why-not-just-learn-from-a-textbook/

TLDR: I learned from those kinds of resources myself, and while I came a long way, for the amount of effort I put into learning, I could have gone a lot further if my time were used more efficiently. That's the problem that Math Academy solves.