Continuity mistake: When we see the "Flabby Patty" for the first time, there are 8 fish in line. When we see it the second time, there is only 5.
Continuity mistake: When SpongeBob scrambles into the Krusty Krab to tell Mr. Krabs the "good news", the doors swing wildly inward. When the two return outside and see the Flabby Patty, the doors have varied from being open inward, to being open outward.
Continuity mistake: SpongeBob is holding a picture of Plankton and Mr. Krabs, then when he pulls Plankton and Mr. Krabs together, the picture disappears.
Chosen answer: You need to provide a little bit more information to be able to answer a question like this. In what region is it not being shown? I see it being replayed here in Australia fairly frequently. As for a general reason, there does not appear to be any for why it specifically might have been taken off the air in any country or region. Like any show certain episodes can sometimes not be replayed for long periods for unknown reasons.
Lummie ★