Answer
You are saying that rain is required only on land, so why does it fall on the sea—but this needs deeper analysis, because the temperature behavior of land and water is different, which influences atmospheric movement, and naturally clouds tend to move toward land due to these variations; my understanding is that, comparatively, the amount of rain falling over the oceans may actually be insignificant relative to their vast size, and your perception might be influenced by observing from a coastal place like Bombay without considering how immense the oceans really are; in reality, water evaporates from the sea, forms clouds, and then those clouds move based on temperature differences and atmospheric dynamics—just as wind moves due to such variations—so the assumption behind your question may itself not be entirely accurate.
