What do you mean, “just the flu”? There are thousands of flu viri and some are much more dangerous than others.
So COVID19 is just another cold, right?
https://en.wikipedia.org/wiki/Influenza_A_virus_subtype_H1N1
Flu viruses are well known, vaccines are available, we have several well test anti-virals that work on it (e.g., Tamiflu), so it has limited downside.
Covid-19 is similar to some cold virus, but many colds are caused by other types, like Rhinovirus. Notice there are no cold vaccines. No one has come up with a working coronavirus vaccine yet. At this point there is large and unknown downside.