The reason the cartoon cat is sad could be that it's feeling lonely or it's facing some kind of danger in its cartoon world.
Maybe it lost its friend or something bad happened to it. That could be why it's sad.
It could be sad because it didn't get the food it wanted or had a bad dream. Sometimes, cartoons don't have a specific reason and it's just for the mood of the story.
Maybe it lost its toy or got separated from its friends.
Maybe the cat is sad because it lost its favorite toy or didn't get enough attention.
It could be that the cartoon cat is sad because it was left alone or had a fight with a friend. Sometimes in cartoons, simple things like that can cause sadness.
It could be that they didn't get the treats they were hoping for or were separated from their friends. Those reasons might cause them to be sad in the cartoon.
The black cat cartoon might be sad because its home was destroyed or it was rejected by its owner. Sometimes, in cartoons, emotions are used to tell a deeper story and make us feel for the characters.
Maybe he lost his favorite toy or didn't get the treat he wanted.
Maybe it lost its favorite toy or got scolded by its owner.
Maybe it tugs at people's heartstrings. The expression of the sad cat makes us feel for it and that's why it gets popular.