What we are observing here is differences in political reasoning style.
Dr. Fauci (whatever else one might think about him) ultimately uses a scientific reasoning style. That means that he analyses the causes of events in terms of likelihood and evidence. Within this scientific worldview, Fauci has always accepted the possibility that the virus originated in some research setting: not necessarily in the Wuhan lab that is consistently cited, but in some human context through some scientific activity. However, there has been precious little evidence available that suggests this is the case, and in the absence of such evidence the likelihood that the pandemic is lab-originated is fairly small, since — as Fauci well knows — labs that deal with such viruses are typically designed with multiple levels of safeguards against accidental release. Moreover (from the scientific perspective), knowing the origin of this virus is of little use in combatting the virus. It doesn't really matter whether the virus was transmitted from bats or pigs, or escaped from a lab, or mutated naturally within humans; the scientific process of analyzing and developing countermeasures and vaccines will go on exactly the same regardless of the source. It may be useful information to prevent future pandemics, but isn't useful in combatting this pandemic.
On the other hand, many people in the political world use a narrative reasoning style. Narrative reasoning by its nature wants to assign causes to human actors; it want to build a narrative in which specific people did or did not do something, the causal result of which was the event in question. Trumpworld in particular has a large share of people committed to narrative reasoning (including Trump himself), to the extent that they are willing to imagine wild human conspiracies to explain events that would otherwise be seen as natural or ordinary. From the beginning of the pandemic, Trump was concerned with developing a narrative — any narrative — in which he and his administration were absolved of responsibility and any need for action with respect to the pandemic or its effects. Trump fixated on the Wuhan lab (after several other less successful narrative gambits) because casting the cause of the pandemic on Chinese malfeasance steered the conversation away from the narrative view that the Trump administration's incompetence or inaction led to the spread of the disease in the US.
One of the unfortunate side-effects of this difference is that Fauci's scientific reasoning often worked against the narrative agenda that Trump wanted to achieve. Fauci was forced to downplay the possibility of a human origin to the pandemic merely because Trump overplayed that narrative, far beyond what was reasonable from any scientific worldview. However, because of Fauci's broad popularity — popularity which was itself a function of Fauci's insistence on scientific reasoning — Fauci was implicated as part of a separate Trumpworld narrative in which human agents were actively working to undercut Trump and his administration. Within that Trumpist worldview Fauci is an 'enemy', and as an enemy he is subject to protracted efforts to defame or undermine his character or respectability. These emails — which I haven't reviewed, but which I'm confident express a typically cautious scientific assessment of the situation — have entered into the Trumpworld narrative as confirmation that Fauci is a malefactor. Honestly, it is more or less irrelevant what the emails actually say. Those who have accepted the narrative that Fauci was working against Trump will accept the emails as proof-positive, regardless of their actual content.