"In the immediate aftermath of the shooting, police officers collected what was initially described as a "manifesto" authored by Hale. David Rausch, the director of the Tennessee Bureau of Investigation, later called the descriptor a "mischaracterization", describing the writings as a document detailing Hale's plan and "journal-type rantings". The MNPD denied requests for the files by The Tennessean and state senator Todd Gardenhire, who argued, along with some open-government advocates, that Tennessee's public records laws required the release of the writings. Metro Nashville Council Member Courtney Johnston said that the FBI had told her that the documents would not be released because they detailed a "blueprint of total destruction" and could inspire other shooters. Several Tennessee politicians and public figures—including Elon Musk and Donald Trump Jr.—publicly called for the release of the documents. Senator Bill Hagerty said, "I think people do deserve to know what took place [and] what was in the mind of this sick person that committed these heinous murders." House Republican Caucus Chairman Jeremy Faison attributed the lack of a legislative response to the shootings to the delayed release, saying, "We cannot possibly address this horrific situation until we know what was in [the] manifesto."

On April 28, 2023, Tennessee Governor Bill Lee announced that, per his communications with Drake, the writings would be released "very soon". When the National Police Association and the Tennessee Firearms Association, separately, filed suit to obtain the writings, the MNPD announced that, in the face of "pending litigation", it would delay the release on the advice of counsel. The Covenant School sought to intervene in both cases to protect "sensitive information owned by The Covenant School" from being released,and a collection of Covenant parents, representing 75% of the families at the school, sought to provide argument that the writings—even in a redacted form—should not be released at all. A judge granted the requests to intervene by the school and the parents."

I think that does answer the why - because, according to those who have seen it, the text doesn't necessarily contain much to explain why Hale did it, but does contain sensitive details about the security at the school. Considering that it's a Christian school, it seems unlikely that the school board and 75 percent of the parents would have taken that position just for the sake of avoiding bad publicity for trans people.

But anyway, I do see what you mean - certainly liberal media channels would be much more reluctant to publish anything that could reflect badly on transgender people, than things that reflect badly on other groups such as conservative Christians. And while I'm more inclined to agree than not with such a stance, I can obviously see why it would look bad to conservatives.