I suspect most people posting in the forum live in urban areas where large animals are rare (except for certain common synanthropic species). Many of us do our nature observing close to home, so the new animals we are most likely to see are arthropods and other small creatures. Even on trips to less human-dominated environments (nature reserves etc.), large vertebrates are shy and not easy to find in many parts of the world – so being able to add such animals to one’s life list is not a common occurrence.
A question: why do you consider that insects and spiders are not animals?