The trigger impulse for many is to assume the refusal as to do with racism. It doesn’t necessarily have to be that reason.
The estate may be protecting the author’s vision of what story was being told.
A similar issue is going on in England theater right now.
Some want a popular black actor Idris Elba to become the next 007 after Daniel Craig finally leaves. For years, Craig has given interviews saying that he ‘hates doing’ the role and wants each movie to be his last, then a few months later, we all find out he has signed on to make yet another 007 film.
As stated, Idris Elba is very popular, Steven Spielberg also wants to see him in that role, but Idris is not of the appearance the original author wrote about in his descriptions; a Scotsman as known in those days.
The estate has a right, even an obligation to guard that brand image.
I wouldn’t want to see a stephen spielberg 007 movie anyhow.