Because it doesn't make sense that it's part of the web share functionality to begin with.
The native share dialog is about "I have this piece of content, now share it with one of these other apps", e.g. saving a document locally, or sending it with AirDrop, or saving to Google Drive, or sending as an email attachment, etc.
Installing a site as an app on your homescreen has absolutely nothing to do with sharing content to begin with.
The native share dialog is about "I have this piece of content, now share it with one of these other apps", e.g. saving a document locally, or sending it with AirDrop, or saving to Google Drive, or sending as an email attachment, etc.
Installing a site as an app on your homescreen has absolutely nothing to do with sharing content to begin with.