Because people’s lives and livelihoods are at stake. If you do something foolish and get covid, you endanger everyone you come in contact with and everyone the people you come in contact with come in contact with.
Plus, as long as the virus isn’t contained, our economy will flounder. People who do unwise things are ensuring continued economic hardship.
But let’s really boil this down. The longer people do irresponsible things - like go to WDW - the longer it will remain irresponsible to go to WDW, and the longer responsible people won’t get to do it.
A raging global pandemic is a really, really good thing to be obsessive about.