There is an interview about te behind the scenes maneuvering to remove the priesthood ban.

https://www.sltrib.com/religion/2024/06/09/lds-prophet-david-o-mckay-came-oh/

Confirms the Brazil temple as the major reason. It does not make J. Fielding, Lee, McConkie, Dyer, packer, or Petersen look very good.

A few semi-random quotes:
"Kimball was ready to lift the priesthood/temple ban months or even years before he did. Why did he wait?

One reason would be that he needed to have consensus in the Quorum of the Twelve [Apostles]. The church teaches that new doctrinal or policy changes need to be unanimous among the highest leaders. It took some time to work with apostles who had reservations."

"In the fall of 1969, Brown has absolutely had it with the [leaders’] inability to change their views. Not with [church President] David O. McKay. McKay would lift the ban if he had consensus among the Twelve, but he doesn’t. So Brown meets in secret with McKay’s sons. He says, “We’ve got to change the policy before your dad dies. Will you help me?” The two sons, David Lawrence and Llewelyn McKay, agreed to it. So they go to the Hotel Utah and convince President McKay, who’s now very old and in poor health. He’s got moments of lucidity."

"What Dyer doesn’t know is that President McKay had already made plans to ordain a Black man to the priesthood by the name of Monroe Fleming. When word [about Fleming’s possible ordination] got to Dyer, it sent off alarm bells. He contacted Harold B. Lee. …Lee nudged or coerced, if you will, McKay into changing his support."

"In December of 1975, Kimball, who was now church president, paid this elderly apostle a visit. Brown, [who was dying] looked [the new president] in the eyes and said, “Promise me you’ll lift this ban,” and Kimball made that pledge but said it would take time."

"After the revelation, Kimball will praise McConkie in private for his support. Then McConkie and [apostle] Boyd K. Packer, a close ally, start to give firesides in the church in which they embellish some of the experiences that happened. They say stuff like, “the [past] church presidents appeared to the Twelve on June 1st.” Jesus himself, Packer said, “appeared and told us that we needed to lift the ban.” When those otherworldly reports filtered back to Kimball, he was furious because that’s not what he said happened."

"When apostle Mark E. Petersen learned that the ban had been lifted, he insisted that an interracial disclaimer would be published next to the priesthood revelation in the [church-owned] Deseret News. It sent mixed messages to Black Latter-day Saints. … They can now enjoy the privileges of the temple, but they’re still being told that they cannot marry interracially.

Some of these views [against interracial marriage] show up in church manuals even as late as 2010 and 2011, when the youth of the church are still being taught to marry within their own race. ..."
"

I suspected that the Brazil temple was the prime mover behind lifting the ban. IIRC, they had to sideline two of the Q12 (I believe Petersen and Stapley) to get them out of the way; one was in the hospital and the other was shunted off to Europe for the final vote.

And since Packer lied about damn near everything anyway, it wouldn't have been a stretch to get him to lie about this too.

Everyone can access the Trib. You get 3-4 free articles before you hit the pay wall. If you've accessed articles and haven't cleared your History and Browser, it retains that and denies access. Click on a Trib article, then when you're on the page, go to the three dots and click on the Trib url. Right click and it will open a box that gives you a choice to select "More from this site" Click on that and it will pull up all the Trib site that are in your History. Delete them. Then hit "Clear Browser History". After that your computer will be cleaned of Trib articles and you get another 3-4 articles.

The Question was:
Revelation -or- change of policy ?

Either alternative had both an Upside & a Downside.

as I recall, this question didn't have a clear-cut answer or response at the time (?), but not much of a topic recently.

Mormons seem very skilled at erasing undesirable parts of their history from members' memories. In the 70s everyone was sure the ban was doctrine based on non-valiance in the pre-existence. So it was up to G-d (not them) to fix it later on sometime. I suspect members now would have a hard time admitting to themselves that people used to sincerely believe this.

Back then Mormon Doctrine was thought of as gospel and none of the leaders pushed back against this. It's a great study in people believing what they want to believe about their own history.