Three things can be blamed for the state of affairs where it tends to be extremely hard to find good online courses on magic.
First is the fact that it is hard to carry out genuinely confidential communication online. Yet if magic training was to be carried out online, some formulas and other highly confidential bits of information would have to be transmitted through these less-than-secure networks. Even if, say, the communication between the magician and the student is taking place through Gmail (www.gmail.com) whose usage instructions are found in this post, you still can’t be sure about all aspects of security. Yet if the magicians are to be believed, it would seem that if some of the secrets they hold were to be revealed to the uninitiated, this world would change in a dramatic way.
Second is the fact that the proper teaching of magic would require some things to be demonstrated practically, and that is not easy to do online.
Third is the fact that most old school magicians (who are the people possessing genuine knowledge of magic) have tended to be tech-phobic, meaning that they are reluctant to embrace the Internet as a tool for training a new generation of magicians.