The big villain is long copyright. Books from the sixties and even the
thirties are still in copyright, their authors are mostly no longer
around to defend them, and the copyrights are in the hands of people who
only want to maximize income from them.
When a work is out of print, anyone can produce a bowdlerized edition,
and someone else can produce an authentic edition, preserving every
illustration, dirty word, and typo from the original.
Another issue is that there's too much focus on words rather than
content today. While researching my blog post on Dahl, I read the
beginning of "The Witches" and was horrified at how the authorial voice
replicates the witch-hunt mentality of the sixteenth and seventeenth
centuries. The narrator stresses how any nice woman the reader meets
might actually be a murderous witch. He says, "Oh, if only there were a
way of telling for sure whether a woman was a witch or not, then we
could round them all up and put them in the meat grinder."
No amount of changing the words, short of completely rewriting the
story, takes that mindset away. The bowdlerized edition has witches
infiltrating society while holding prestigious jobs rather than
low-level ones, but that changes nothing.
In the original version of "Charlie and the Chocolate Factory," the
Oompa Loompas were African Pygmies. He changed that one himself (under
pressure), but nothing takes the creepiness away from having foreign
workers who can never leave the factory.
We need to understand these authors for what they were rather than
covering them up with cosmetic changes.