Great, as a parent you are free to read whatever books reflect your values to your children.
If the plight of the fictional Oompa Loompas (I don't recall slavery being justified in the book, but hey, your interpretation is as good as any, that's the wonderful thing about books) is upsetting to you -- do not read or expose your kids to it.
Expose them to books that reflect your values. Or even write new ones if you have any talent.
Editing existing books in this manner is never necessary or justified.
Sales are relevant, and sales are down. Another version that sells better has no impact on the copy on your shelf.
(... and if they can goose sales by generating market buzz via controversy, more power to them. A tip of my hat to playing folks like us against each other to put coin in their pockets. ;) ).
This fact isn't some kind of attack on history; it's a reflection of the fact that the stories we tell children change to reflect our values.
This publisher is in the business of selling new copies of stories for children. It'd be surprising if they didn't change.