Why is it that everyone brings melons when they are visiting a character in the hospital?
The origin of this is actually in real life.

In Japan, melons are considered to be a rather expensive fruit, and after often given as gifts, specifically when visiting someone in a hospital. I'm not really sure how this particular notion was started, just that it is a common thing nowadays.



In fact, here is a 21,000-yen (~$210) melon:



It would seem that the anime and manga that feature this idea are simply drawing from this part of Japanese culture.