Simply put, it’s because they aren’t as intelligent as us, so their sense of pleasure isn’t as sophisticated. Art, cuisine, discovery, if you think about it all of those things really only exist because humans are smart enough to question their environments and the world around them.
Most animals don’t have that luxury. They don’t care about variety because they literally don’t know what it is, they’re just happy to have a meal. That’s the same reason why cats can spend hours doing seemingly nothing and still be happy (they don’t have concepts of boredom like we do).
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