In short, "what HEAVEN'S GATE is actually famous for" is already well-known and has been spoken of ad nauseum for decades, this release is supposed to be about letting the film speak for itself. All that negative material is readily available, as is Bach's book.
If Heaven's Gate weren't such a scandalous bomb, it wouldn't be remembered at all today and certainly wouldn't be inducted into the Criterion Collection for reappraisal. To present it with hardly any context of what the movie is actually notable for is, at the very least, a missed opportunity.
Criterion has long striven to provide context for the importance of each of the movies they induct into the Collection, but in this case they kowtowed to Cimino's bruised ego. That's a disappointment.