Browsing throughout those courses I found out that more then 50% of them require you to either sign in with FB or Google in order to access them, so no thank you. Remember, if something is free then you're the product.
By having a FB/Google sign in a website won't have to deal with implementing login, registration, email verification, forgotten passwords, etc.
Oh and even better; if they get hacked then all the hackers will be left with are hashed FB/Google IDs.