I am just puzzled why delifue calls something that, as far as I know is pretty standard across the industrie, bad practice

There's 2 cases being discussed. A UUIDv7 is a bad secret, but it's fine for many other ids. If I can guess your user id, it shouldn't really matter because your business logic should prevent me from doing anything with that information. If I can guess your password reset token it's a different story because I don't need anything else beyond that token to do damage.

Because it is?