That assumes there is not enough money for everything. Also, it assumes that the disaster fallout will not impact those other things. We are seeing quite clearly a spill-over from the pandemic into other aspects of human wellfare, and you don't have to have COVID-19 to suffer the consequences of its presence.

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The issue is, as I said in my previous post, that our society is generally close to "maximum capacity" in a variety of different ways.
It's not that people (governments included) are ignorant or arrogant about the possibility of bad things happening.
It's simply that there's always a heap of more mundane things that definitely are happening which require their time, effort and money to deal with.
I absolutely agree that the effects of a disaster are likely to be more damaging than the cost of preparation.
The problem is, a government that plans to spend money on stuff that
might happen instead of spending it on stuff that definitely
is happening all the time probably isn't going to be that popular.
Doesn't really matter which side of the political fence you sit on.
A party that announces they plan to spend a heap of money on disaster prevention
is going to get labelled as a bunch of "loony doomsday preppers" by their opponents and they're probably going to lose
some support of their own voters as well.
Let's face it, everybody's a political NIMBY.
Tree-huggers are going to be happy with money spent on disaster prevention
unless it reduces funding for environmental projects.
Workers are going to be happy with money spent on disaster prevention
unless it reduces funding for industry.
Parents are going to be happy with money spent on disaster prevention
unless it reduces funding for education.
Unemployed people are going to be happy with money spent on disaster prevention
unless it reduces funding for welfare.
Etc.
It'd be nice if this C19 epidemic
did compel governments to make better plans but, at the end of the day, when they've got voters screeching about a variety of immediate concerns, I wouldn't count on it.