Other forms: falling through the cracks; fell through the cracks; fallen through the cracks; falls through the cracks
A task or situation will fall through the cracks if the people who are supposed to do something about it don't notice or remember, so nothing gets done. Like when your birthday ends up falling through the cracks because everybody forgot!
Imagine something small and thin, like a slip of paper, falling through the narrow space between your desk and the wall and getting lost or forgotten. That’s the image suggested by the idiom fall through the cracks. It’s not that people don’t care about a task, they just fail to notice or remember until it’s too late, because so many other, more obvious things are taking up their attention. This often happens in large organizations. Fall between the cracks is another form of the idiom.