Because they forgot the four chords: https://www.youtube.com/watch?v=5pidokakU4I
Actually, 3 chords are all you need and sometimes 2 will suffice!
https://www.guitartricks.com/blog/10-Famous-Songs-with-Three-Chords-or-Less
https://www.nme.com/blogs/nme-blogs/12-amazing-songs-with-just-three-chords-7381
https://www.thoughtco.com/two-chord-songs-that-were-big-hits-2523852