Honestly, taking AP Music Theory in high school allowed me to learn anything else I wanted on my own without going to music college by reading books on topics (jazz harmony, orchestration, counterpoint, etc.), studying scores, transcribing, and just playing in live settings such as jazz combos and community pit orchestras. My friends who went to music college tell me that they think I know more theory than them!
Once you get past the initial hurdle of learning to read music and understanding the basics of key signatures and how to build chords, everything past that is not difficult to learn, it just simply takes time (maybe it's an expedited process for those who go to school for music, but like Anne said, it's not a necessity for everyone and you can learn it independently). Great video!