While you are absolutely right, I want to highlight that this was done in a quite sophisticated way. It's actually the real login page of Facebook in a webview. I have 2FA on all my accounts including FB, so it looked very legit. Once you have logged in, they seem to grep the token and close the webview.
Some Google auth cookies can only be used on the same tls session that created them[1]. That means the TLS session resumption information (which can be tied to hardware platform features like the TPM) is required to make use of a stolen auth cookie. Unfortunately while that approach has big security benefits, it's pretty anti-user-privacy.
[1]: https://nakedsecurity.sophos.com/2018/10/25/could-tls-sessio...