There is a problem: it is wildly inaccurate. Electrons do not fly in definite orbits; this fact has been known for a very long time. The first three electrons would not be at the same energy level; this fact has also been known for a very long time.
But it is an enormously effective teaching tool, despite all of the falsehoods, and so has spread to every school on the planet.
Great teachers know how to recognize, use, and create these useful simplifications. It is a rare and valuable artistic skill. What other useful simplifications do you know?
P.S. To the nerds out there, here is a slightly less simple representation of the lithium atom. Imagine teaching 7th graders the basics with this image. (photo credit: Clive Freeman, The Royal Institute/Science Photo Library)
P.P.S. It is still a simplification, as is everything you know.