Because:

The XML Paper Specification (XPS) document is a document format, which can be used to view, save, * * * enjoy, protect and digitally sign your document content. XPS documents are like electronic paper: you can't change the content on the paper after printing, and similarly, you can't edit the content of XPS documents after saving in XPS format. In Windows, you can create XPS documents in any program that can print, but you can only view XPS documents in XPS Viewer, sign XPS and set permissions.

you can also set permissions on your XPS document, and no one can view, copy, print or digitally sign the document without your authorization. You can set time limit for permissions, and set the permissions of other users according to your own wishes, so that different users have different access levels.

xps is a document similar to pdf, and cannot be edited after the document is created.