Likely a number of things. 1) Testing has dropped sharply, so if you're not looking for cases, you won't find them. By the same token, if and when testing goes back up, so will the case count, despite the rate of hospitalizations and deaths. 2) The season. These types of infectious diseases are highly seasonal. 3), the natural immunity the population has developed by widespread exposure.
You probably wanted me to say the vaccine is responsible. It may be only partly responsible. I didn't watch all the YouTube video with the graphs. I noticed, though, that covid deaths were already in decline when the vaccinations started, and the rate of decline seemed unaffected by the rate of vaccinations.