Plenty of folks still took them on their own volition.
doesn't matter if even 20% of the population (which is a very high estimate) use some of these measures. You can't explain that the evolution is exactly the same as a Norway...
If you get a disease's R0 below one, it goes away.
Enough people changed their behavior in both countries to make flu go away, because it no longer spread quickly enough to sustain itself.