1. It is a topical "trick" so you get hits by making a video on the subject and make money.
2. You can use the video to show how the technique doesn't work and then sell people a commercial-grade bottle cutter.
RONCO sold a bottle cutter back in the 1970's. Even back then, this was a pretty poor economic proposition.
Just because something is on a YouTube video doesn't mean it is a good idea. And these "tips and tricks" videos are just clickbait to get people to watch the channel and garner advertising dollars. Sadly, the YouTube algorithm often lets junk like this float to the top of their septic tank.
Anyway, we tried this technique and found it was hardly a good way to cut bottles into glasses. We had fun emptying the bottles, though!