No Loot for You! - The Irritating Oversight in ESO High Isle's World Bosses

ESO's High Isle chapter has already been out for over a week, so players have had quite a bit of time to get stuck into it by now. 

Some adventurers have unfortunately ran into problems with the World Bosses in the new Île-Haute et Amenos zone which is proving to be quite bothersome. 

But what's the problem here, exactly?

Falling Afoul of ESO's Loot Limit