Why i cannot save, the saved password, into the password manager as a plain text file?

Why i cannot save, the saved password, into the password manager as a plain text file, and i have to expose it to other maybe malicious apps by copying it? Since it could be used to store not only passwords, but maybe also (for example) encryption Private keys, since there (seem to me) is no limit (that's very good and fantastic!) on how the stored password is. So, into the screen i can only copy the "password". That expose it to all others apps. The same goes for desktop browser. Why not to add the possibility to upload a password from a file? And to save the saved password as a file? Thank You guys!