The flu is less virulent, less deadly, and most people get flu shots which creates herd immunity.
So just because their current flu countermeasures don't include the measures proposed doesn't mean that it's not rational to consider them. Their prior actions could actually be irrational, and the context shift is just allowing them to adjust their perception and actions.
The second is that since WFH is an preventative measure designed to minimize the probability of COVID-19 reaching flu transmission rates, you can't simply say that "the current risk is low", you have to try to consider the likelyhood of risk significantly increasing without action.
Let's be real here, even if COVID-19 was literally exactly a different flu, it would be still be a problem and we should be planning for it carefully. North American hospitals are cost conscious and therefore typically only have enough resources to just about cover a normal flu season spike. Doubling (say nothing about 10x) the amount the hospitalizations required would be an incredible stress to the system.