I think something you're failing to account for in peoples' reactions these figures is that the relationship between their moral transgressions and their work is not spurious.
Feynman was a notable scientist but he was also one of the most famous scientists, he was a great populizer of science especially later in life. Finding out he was a sex pest or womanizer or worse has tangible consequences to that role. Was he a good mentor in general, or only to women he wanted to fuck? Or only ones he didn't? Were there any women pushed out of science because of his inappropriate attention or advances? We now have to ask these questions, and their answers can retroactively change how we evaluate his later life's work as an advocate of science.
Similarly woody allen makes movies that are compelling because of their portrayal of human connection and vulnerability. As you said, what woody allen is accused of is a great crime, far far beyond routine human flaws. It does change the context and the meaning of the movie to know that this is what its creator thinks of human connection as well. You can decide not to believe the allegations, but for people who do believe them I don't think it's an error or transgression for them to evaluate his movies in light of them.
And it is certainly not true that no one criticized these figures before their "faults" were known. Orson Welles famously with woody allen, Picasso was not always revered, and I disliked feynman from reading his own memoirs. It's just these criticisms are not generally welcomed or amplified for figures in the prime of their accolades. Which is an interesting subject itself, I think.