I have no insight into the minds or motivations of the 30 for 30 producers nor do I have any editorial control on the documentary in question and there does not appear to be any Soviet style purging in the making of the documentary.
Of course, to you there likely would not seem to be any Leftist purges of history going on, leftists would see it as completely justified and not a purge, as you apparently do, and likely for the same reasons.
Why is it that you see it as justified?
Correct. You have no insight. You obviously have never worked in the business.