I think people kept it taboo for as long as they could because: people were literally dying due to low vaccination rates, which were caused in large part by such specious conspiracy theories. Fact checkers did not do a 180, it is still widely considered a conspiracy theory, and its very existence harms public health even if there's a remote possibility it's true.

https://en.wikipedia.org/wiki/COVID-19_lab_leak_theory

“Some scientists agree that the possibility of a lab leak should be examined as part of the ongoing investigations into the origin of COVID-19, though they have expressed concerns about the risks of politicization.”