They don't have a big red light saying that it is a treifa. Someone needs to screen it then someone needs to pasken on it whether or not it is a treifa. When it is done on a mass scale it is more likely to get by. When it is a lower level hechsher that also raises questions as to whether or not you trust their psak on the treifa. That makes a hechsher much more of a problem than the woman in the shtetle who checked one chicken and brought any shailo to the local rov not less of a problem. The rabbonim hamachshirim of slaughterhouses will be the first to tell you this.
Again, you are avoiding the issue. The premise here is that they ARE reliable when it comes to paskening trayfus. To remind you, we are going on the assumption that people rely on them for poultry. If they can be relied upon for mass scale chickens, it would seem to be logical that they can be relied upon to pasken goose liver where 1. It's probably not produced on a mass scale and 2. They are more likely to check better than a chicken since there is a higher probability of a traifah.
Not sure what you are not getting, but if you can provide a logical argument as to why it's more complicated for a kashrus organization to certify a goose liver over a regular chicken, I'm all ears.