The problem is that the people admitting these mistakes were not necessarily the political figures advocating them to the populace at large. I imagine a fair bit of opposition to the safe vaccines we are able to enjoy is due to skepticism of political figures not owning up to their initial false statements. For example, I distinctly remember the former president stating loudly and repeatedly that Coronavirus was no big deal (paraphrasing), that it would disappear overnight, that the United States was well prepared for it, and so on. I do not recall any mea culpa's being issue: just one new bold statement after the next.

To be fair to our conservative friends, I'm sure this behavior is not limited to only one political party.

Only after being left with no choice or when politically convenient. Too little too late.

I'm not sure that's actually the case here; anecdotally, but a lot of the criticism of the former president at the time came from his bold statements that he never bothered to correct. Though, to be fair, that's probably not the only reason his former supporters did not come out to vote for him in round 2.