I was puzzled why I - and so many others - am so enamored of this cartoon. After a little thought, here are some conclusions:
Spongebob lives at the bottom of the sea. He, and everyone else there, are safe. They have the entire sea to protect them from the outside world. Symbolically, the sea stands for a preconscious (child-like) state, and for the feminine (the womb). Think of Father Sky and Mother Earth. This makes sense, because Spongebob is in many ways an innocent child, safe in the womb of the ocean. You can say he lives in the Garden of Eden, in a womb which shelters and protects.
Spongebob lives in a world which he experiences with little fear or anxiety. His greatest worry is if he can make a krabby patty the right way. The mythological image of Spongebob is the puer aeternus - the one who is forever a child.
The sea actually has a positive and negative archetype. One is that of creation and the womb; the other is that of death and fear. Both are shown in baptism, in which both death and life are illustrated. In Spongebob, only the positive archetype exists.
I believe the above essentially answers the question of why Spongebob is so popular. He dwells in a Garden of Eden state of innocence, in a safe, well-protected neighborhood. There is something in almost all of us which responds to such a life. The cartoon is actually about reversing the Fall.
People can live with some aspects of their personality still in this state of innocence. I believe the public reception given Spongebob indicates that many Americans identity with this as a not-far-from-ideal life. It's safe and weird. What more can you ask for?
What true danger that exists for Spongebob and his friends comes from outside the sea. The archetype of the horror story is illustrated: something good invaded by something bad. The sea is good; the outside world is a danger.
In the episode titled "Hooky," Spongebob and his dimbulb friend Patrick play on fishermen's hooks dangled from a wharf above the sea. Both are so innocent they don't realize the danger involved, even though Patrick does say that someone who had been playing on them was no longer there. The inference is that he was hauled out of the sea, caught on a hook.
Squidward finally cures Spongebob of his foolishness by stabbing a hook through his pants, making Spongebob think he's going to be hauled up. In literature, this is called Innocence to Experience.
The complete theme of Innocence to Experience is Innocence/Unconsciousness/the Natural State versus Experience/Consciousness/the Machine State. The former are supposed to be characteristics of the Garden of Eden; the later, of the Fall. You can see these themes in H.G Well's The Time Machine, in which the Eloi stand for the innocent, unconscious dwellers in a Garden of Eden, and the Morlocks are the experienced, conscious users of machines.
You can also see these themes in the movie, The Elephant Man, which starts out with a worker severely injured by a machine. Through all of these horrors, the Elephant Man still maintains his innocence.
To a degree, these themes are a bit fraudulent, since they are opposed to technology. But since they exist in many stories and movies, it is best to be aware of them.
You can see these themes in Spongebob, since the outside world is where most of the advanced technology exists. Such as the hooks. Technology does exist in Spongebob's world, but it's not portrayed as dangerous.
In Spongebob's world, there appears to be no State. There appears to be no government, for that matter. Everything is taken care of by Society; this is why the older and wiser Squidward has to teach Spongebob a lesson about the hooks. The older teach the younger, which is as it should be.
Again, we're back to the archetype of the horror story. Society, which is but a thin, fragile film on a bunch of sometimes very unpleasant human nature, is easily damaged by the intrusion of the State. When this happens, all the badness inherent in humanity pops up. Since there is no State in Spongebob's world, everything is Society. Everything is held together by what the British statesman Edmund Burke called "the little platoons" - the social groupings like family, friends, neighborhoods and churches that glue societies together.
Burke's idea is of course anathema to those who view as the State as a god capable of working wonders. In reality, the State is a horror.
The cartoon is in some ways a "conservative" cartoon. Everyone is imperfect. Spongebob himself suffers a bit from what appears to be Obsessive-Compulsive Disorder. In the episode "Pickles," Bubble Bass lies and tells Spongebob there were no pickles on his krabby patty. Spongebob is then up all night making burgers, trying to figure out what he did wrong. In the end, Bubble Bass is exposed for a liar, and everything ends well.
Actually, you can call Spongebob Squarepants a conservative libertarian cartoon. There is no State, indeed no government, and everyone is imperfect.
I've seen this portrayal of a libertarian/conservative society in other cartoons. It exists in The Simpsons, which celebrates family and friends, and denigrates politics. The line from the program I can never forget is when Chief Wiggum says, "I didn't say the government couldn't harm you. I said it couldn't help you." Truer words have never been spoken.
There are, thank God, no politics in Spongebob's world. >From this you can infer that in as perfect of a world as can exist, there would be no politics or politicians. What politics that does exist in Spongebob's world would have to be outside the sea, in the world where the hooks came from. In his world, there are no wars, which are always caused by the State. There are just the usual human frailties, such as Bubble Bass' lies and Spongebob's own childishness.
Ezra Pound called artists "the antenna of the race." He was, I believe, exactly right.