I just saw a question where someone clarified what OP is asking in the Staging Ground then approved the post to publish it on the main site, and I thought it's kind of strange that they would make drastic changes themselves instead of giving OP feedback on the Staging Ground, but whatever. What I'm more confused about is that the post on the main site doesn't show that OP's words have been changed – in fact, isn't that required by the CC-BY-SA 4.0 license? IANAL, but the license does say "You must ... indicate if changes were made."
Correct me if I'm wrong, but OP submits content to the Staging Ground under the CC license, meaning the system needs to indicate if anyone besides OP has modified the content. Now that I think about it, the system needs to "give appropriate credit" to the editors too, since they submit their edits under the CC license.
I looked around but the most relevant thing I found was this from Yaakov Ellis (added bold):
The Staging Ground is designed to have big differentiations from the public site in order to foster an environment with lower stakes, where Reviewers will feel less of an urgency to respond (with downvotes, comments, and edits) in manners that can at times add pressure upon new users. As such, neither revision history records nor comments from Staging Ground questions will be transferred to the newly published questions. The only indicator that posts originated in the Staging Ground will be a
PostHistoryentry relating the newly published post back to the original Staging Ground post, which will only be visible in the Timeline to Reviewers.