Notice I didn't say for EVERY things. Only relevant things. That player would probably expect to have result from interacting with. It is done for fishing racks, some flowers, some animals, some log piles. Finish it for the other stuff, if it is not done already.
Are you assuming that this would take no time or effort to do, or that Larian has unlimited resources?
What I am assuming is that Larian created a strong RPG engine that allows to easily change such obvious things as loot/drops, which are an important part of any RPG, IMHO (because of course, some people will prove me wrong, and that loot/drops is absolutely irrelevant in a decent RPG for most players...).
My first disappointment with DoS came when I first tried to interact with the fishing nets on the beach. Nothing. It was a terrible desillusion, and I knew something was wrong, and maybe it wasn't the interactive and "deep" RPG I had expected.
