Metadata and location data is lost when adding photos to iCloud shared album

You are right, it is very clumsy and inconvenient to have to add all metadata again to a photo when sharing it in a shared album. It used to be different in the earlier versions of sMacOS X. Photos arrived in the shared albums with all metadata attached. Apple removed the sharing of the metadata intentionally several years ago, probably because of security reasons. You may not mind to share all metadata you diligently added to the shared photos, but a person shown in the photo might mind. If you publish the shared album as a public website, any person depicted in one of your photos might request from Apple that the metadata will be stripped from the photo or the photo removed. This could create a lot of work for Apple's legal department.

If you upgrade to Catalina you can share your photos in a folder on iCloud Drive instead. On iCloud Drive you can share the photos with all metadata and in the original quality. In a shared album we can only share the photos at a reduced size, up to 2048 pixel at the longest edge. That is not sufficient, if we want to share the photos a a high quality.

You are talking to other users, not Apple. If you want Apple to hear your suggestion, make it through their defined portal for such ideas: Product Feedback - Apple