This being March 2nd, not February 2nd, I'd say that the causes include:
* Ever-increasing numbers of people who have recovered and thus have "natural" immunity;
* Ever-increasing numbers of people who have been vaccinated (on February 2nd this population was much less significant);
* People adjusting their habits ... maybe.
Herd immunity is not like a switch, it's a trend. Between recovered people an those vaccinated, we are steadily approaching the point where the population of the susceptible is small and sparse enough that Covid will become rare. Herd immunity will also mean that new variants will become fewer as the hosts necessary for variant-producing mutations become fewer.