Except when it's not implemented properly and it breaks other workflows. For example, if it only shows a button (not a link or a tag) and copies the link to the clipboard via JavaScript, consider this scenario: I want to send this "link" to my other computer using Firefox's built-in Send Page to Device feature. I have to click Share, click the copy to clipboard button, open a new page, paste the URL, and only then can I share it.

If the state were stored in the URL, I could do it in two steps: open context menu -> Send Page to Device, and I'm done.