That’s because everyone expects that it’s so obvious from watching the video that it doesn’t need to be explained.
Thumb through slap has gained much more popularity/exposure over the last 3 or so years and there are many more videos discussing it now. Victor Wooten’s old slap video is great and his newer one is really good too.
Many adults need to rediscover and embrace how children learn… you conduct experiments, observe the results, make changes and repeat until you’ve achieved your goal. You have a thumb, you have some strings, you keep hitting one against the other until you get what you want. 