If they could admit they had made a mistake by not addressing this issue (again publicly in 89), they would gain some credibility.
To be fair, the current people in the USGA can't really admit that they were wrong. It'd be like a current President trying to "admit" that a former president was wrong (or right) about something. There's "the office" or "the institution" and then there are the actual people that fill those roles.
"The USGA" screwed up, but "Mike Davis" did not.
They being the USGA, not the people that run it. Does anyone really know who they are if you are not really involved (unlike a former President). There would be absolutely nothing wrong with saying something like this:
"While hindsight is 20/20, we, as the governing body of golf, had missed an opportunity to properly address this in the past..." I don't see the harm in it and it accomplishes something (admittedly I am not sure if anyone can quantify what that something may be).