Because they had evidence that made the wet market theory the one most likely to be true, and a lack of stronger evidence for the lab leak theory. Investigating and supporting the theory that is best supported by the evidence you have isn't crazy, it's science.
When you look at all the facts you have, and then ignore that because it doesn't support what you want to be true, and then you act on what you wish was true instead, that's crazy. That's exactly what Trump and many of his supporters were doing.
We have new evidence now that suggests the lab leak theory is more likely than the wet market one, so once it is released non-crazy people will support the lab leak theory when they could not (and should not) have before.