did the flu and cold just magically disappear?
The run of the mill flu is exponentially harder to spread than Covid19.
Given all the precautions we are taking against Covid19 right now the flu is effectively being wiped out because the chain of transmission is being *entirely* broken.
In regular times, unmasked people go around all day coughing and sneezing all winter, touching everything, etc etc etc...and it spreads. This year with everyone wearing masks inside, a lot of cleaning, and a lot of handwashing, it just can't spread.
So yeah, it's mostly disappeared, but there was certainly no "magic" involved.