It may be that the SmartObject is rendered by ACR thus the metadata is no longer needed.
I think it's more that the exported image is the original placed image. I think ACR is still using metadata when editing the smart object but that is not exported. I don't see how ACR could know the current settings of the smart object without using the embedded file's metadata. I don't think ACR is rendering each edit. I think that just the current settings are used. Otherwise the edits would not be non-destructive.
Also although the exported file has the ACR settings used when the file was placed in the smart object the metedata property crs:AlreadyApplied is set to false and no, the settings are not yet applied. They would be applied the next time the file is opened in Photoshop unless the settings were removed first.